/**************************************************************************
 *
 * Copyright 2013-2014 RAD Game Tools and Valve Software
 * Copyright 2010-2014 Rich Geldreich and Tenacious Software LLC
 * All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 *
 **************************************************************************/

// File: rg_etc1.cpp - Fast, high quality ETC1 block packer/unpacker - Rich Geldreich <richgel99@gmail.com>
// Please see ZLIB license at the end of rg_etc1.h.
//
// For more information Ericsson Texture Compression (ETC/ETC1), see:
// http://www.khronos.org/registry/gles/extensions/OES/OES_compressed_ETC1_RGB8_texture.txt
//
// v1.03 - 5/12/13 - Initial public release
#include "vogl_core.h"
#include "vogl_rg_etc1.h"

#include <stdlib.h>
#include <memory.h>
#include <assert.h>
//#include <stdio.h>
#include <math.h>

#if defined(COMPILER_MSVC)
    #pragma warning(disable : 4201) //  nonstandard extension used : nameless struct/union
#endif

#if defined(_DEBUG) || defined(DEBUG)
#define RG_ETC1_BUILD_DEBUG
#endif

#define RG_ETC1_ASSERT VOGL_ASSERT

namespace vogl
{

    namespace rg_etc1
    {
        typedef unsigned char uint8_t;
        typedef unsigned short uint16_t;
        typedef unsigned int uint32_t;
        typedef unsigned int uint32_t;
        typedef long long int64_t;
        typedef unsigned long long uint64_t;

        const uint32_t cUINT32_MAX = 0xFFFFFFFFU;
        const uint64_t cUINT64_MAX = 0xFFFFFFFFFFFFFFFFULL; //0xFFFFFFFFFFFFFFFFui64;

        template <typename T>
        inline T minimum(T a, T b)
        {
            return (a < b) ? a : b;
        }
        template <typename T>
        inline T minimum(T a, T b, T c)
        {
            return minimum(minimum(a, b), c);
        }
        template <typename T>
        inline T maximum(T a, T b)
        {
            return (a > b) ? a : b;
        }
        template <typename T>
        inline T maximum(T a, T b, T c)
        {
            return maximum(maximum(a, b), c);
        }
        template <typename T>
        inline T clamp(T value, T low, T high)
        {
            return (value < low) ? low : ((value > high) ? high : value);
        }
        template <typename T>
        inline T square(T value)
        {
            return value * value;
        }
        template <typename T>
        inline void zero_object(T &obj)
        {
            memset((void *)&obj, 0, sizeof(obj));
        }
        template <typename T>
        inline void zero_this(T *pObj)
        {
            memset((void *)pObj, 0, sizeof(*pObj));
        }

        template <class T, size_t N>
        T decay_array_to_subtype(T (&a)[N]);

#define RG_ETC1_ARRAY_SIZE(X) (sizeof(X) / sizeof(decay_array_to_subtype(X)))

        enum eNoClamp
        {
            cNoClamp
        };

        struct color_quad_u8
        {
            static inline int clamp(int v)
            {
                if (v & 0xFFFFFF00U)
                    v = (~(static_cast<int>(v) >> 31)) & 0xFF;
                return v;
            }

            struct component_traits
            {
                enum
                {
                    cSigned = false,
                    cFloat = false,
                    cMin = 0U,
                    cMax = 255U
                };
            };

        public:
            typedef unsigned char component_t;
            typedef int parameter_t;

            enum
            {
                cNumComps = 4
            };

            union
            {
                struct
                {
                    component_t r;
                    component_t g;
                    component_t b;
                    component_t a;
                };

                component_t c[cNumComps];

                uint32_t m_u32;
            };

            inline color_quad_u8()
            {
            }

            inline color_quad_u8(const color_quad_u8 &other)
                : m_u32(other.m_u32)
            {
            }

            explicit inline color_quad_u8(parameter_t y, parameter_t alpha = component_traits::cMax)
            {
                set(y, alpha);
            }

            inline color_quad_u8(parameter_t red, parameter_t green, parameter_t blue, parameter_t alpha = component_traits::cMax)
            {
                set(red, green, blue, alpha);
            }

            explicit inline color_quad_u8(eNoClamp, parameter_t y, parameter_t alpha = component_traits::cMax)
            {
                set_noclamp_y_alpha(y, alpha);
            }

            inline color_quad_u8(eNoClamp, parameter_t red, parameter_t green, parameter_t blue, parameter_t alpha = component_traits::cMax)
            {
                set_noclamp_rgba(red, green, blue, alpha);
            }

            inline void clear()
            {
                m_u32 = 0;
            }

            inline color_quad_u8 &operator=(const color_quad_u8 &other)
            {
                m_u32 = other.m_u32;
                return *this;
            }

            inline color_quad_u8 &set_rgb(const color_quad_u8 &other)
            {
                r = other.r;
                g = other.g;
                b = other.b;
                return *this;
            }

            inline color_quad_u8 &operator=(parameter_t y)
            {
                set(y, component_traits::cMax);
                return *this;
            }

            inline color_quad_u8 &set(parameter_t y, parameter_t alpha = component_traits::cMax)
            {
                y = clamp(y);
                alpha = clamp(alpha);
                r = static_cast<component_t>(y);
                g = static_cast<component_t>(y);
                b = static_cast<component_t>(y);
                a = static_cast<component_t>(alpha);
                return *this;
            }

            inline color_quad_u8 &set_noclamp_y_alpha(parameter_t y, parameter_t alpha = component_traits::cMax)
            {
                RG_ETC1_ASSERT((y >= component_traits::cMin) && (y <= component_traits::cMax));
                RG_ETC1_ASSERT((alpha >= component_traits::cMin) && (alpha <= component_traits::cMax));

                r = static_cast<component_t>(y);
                g = static_cast<component_t>(y);
                b = static_cast<component_t>(y);
                a = static_cast<component_t>(alpha);
                return *this;
            }

            inline color_quad_u8 &set(parameter_t red, parameter_t green, parameter_t blue, parameter_t alpha = component_traits::cMax)
            {
                r = static_cast<component_t>(clamp(red));
                g = static_cast<component_t>(clamp(green));
                b = static_cast<component_t>(clamp(blue));
                a = static_cast<component_t>(clamp(alpha));
                return *this;
            }

            inline color_quad_u8 &set_noclamp_rgba(parameter_t red, parameter_t green, parameter_t blue, parameter_t alpha)
            {
                RG_ETC1_ASSERT((red >= component_traits::cMin) && (red <= component_traits::cMax));
                RG_ETC1_ASSERT((green >= component_traits::cMin) && (green <= component_traits::cMax));
                RG_ETC1_ASSERT((blue >= component_traits::cMin) && (blue <= component_traits::cMax));
                RG_ETC1_ASSERT((alpha >= component_traits::cMin) && (alpha <= component_traits::cMax));

                r = static_cast<component_t>(red);
                g = static_cast<component_t>(green);
                b = static_cast<component_t>(blue);
                a = static_cast<component_t>(alpha);
                return *this;
            }

            inline color_quad_u8 &set_noclamp_rgb(parameter_t red, parameter_t green, parameter_t blue)
            {
                RG_ETC1_ASSERT((red >= component_traits::cMin) && (red <= component_traits::cMax));
                RG_ETC1_ASSERT((green >= component_traits::cMin) && (green <= component_traits::cMax));
                RG_ETC1_ASSERT((blue >= component_traits::cMin) && (blue <= component_traits::cMax));

                r = static_cast<component_t>(red);
                g = static_cast<component_t>(green);
                b = static_cast<component_t>(blue);
                return *this;
            }

            static inline parameter_t get_min_comp()
            {
                return component_traits::cMin;
            }
            static inline parameter_t get_max_comp()
            {
                return component_traits::cMax;
            }
            static inline bool get_comps_are_signed()
            {
                return component_traits::cSigned;
            }

            inline component_t operator[](uint32_t i) const
            {
                RG_ETC1_ASSERT(i < cNumComps);
                return c[i];
            }
            inline component_t &operator[](uint32_t i)
            {
                RG_ETC1_ASSERT(i < cNumComps);
                return c[i];
            }

            inline color_quad_u8 &set_component(uint32_t i, parameter_t f)
            {
                RG_ETC1_ASSERT(i < cNumComps);

                c[i] = static_cast<component_t>(clamp(f));

                return *this;
            }

            inline color_quad_u8 &set_grayscale(parameter_t l)
            {
                component_t x = static_cast<component_t>(clamp(l));
                c[0] = x;
                c[1] = x;
                c[2] = x;
                return *this;
            }

            inline color_quad_u8 &clamp(const color_quad_u8 &l, const color_quad_u8 &h)
            {
                for (uint32_t i = 0; i < cNumComps; i++)
                    c[i] = static_cast<component_t>(rg_etc1::clamp<parameter_t>(c[i], l[i], h[i]));
                return *this;
            }

            inline color_quad_u8 &clamp(parameter_t l, parameter_t h)
            {
                for (uint32_t i = 0; i < cNumComps; i++)
                    c[i] = static_cast<component_t>(rg_etc1::clamp<parameter_t>(c[i], l, h));
                return *this;
            }

            // Returns CCIR 601 luma (consistent with color_utils::RGB_To_Y).
            inline parameter_t get_luma() const
            {
                return static_cast<parameter_t>((19595U * r + 38470U * g + 7471U * b + 32768U) >> 16U);
            }

            // Returns REC 709 luma.
            inline parameter_t get_luma_rec709() const
            {
                return static_cast<parameter_t>((13938U * r + 46869U * g + 4729U * b + 32768U) >> 16U);
            }

            inline uint32_t squared_distance_rgb(const color_quad_u8 &c) const
            {
                return rg_etc1::square(r - c.r) + rg_etc1::square(g - c.g) + rg_etc1::square(b - c.b);
            }

            inline uint32_t squared_distance_rgba(const color_quad_u8 &c) const
            {
                return rg_etc1::square(r - c.r) + rg_etc1::square(g - c.g) + rg_etc1::square(b - c.b) + rg_etc1::square(a - c.a);
            }

            inline bool rgb_equals(const color_quad_u8 &rhs) const
            {
                return (r == rhs.r) && (g == rhs.g) && (b == rhs.b);
            }

            inline bool operator==(const color_quad_u8 &rhs) const
            {
                return m_u32 == rhs.m_u32;
            }

            color_quad_u8 &operator+=(const color_quad_u8 &other)
            {
                for (uint32_t i = 0; i < 4; i++)
                    c[i] = static_cast<component_t>(clamp(c[i] + other.c[i]));
                return *this;
            }

            color_quad_u8 &operator-=(const color_quad_u8 &other)
            {
                for (uint32_t i = 0; i < 4; i++)
                    c[i] = static_cast<component_t>(clamp(c[i] - other.c[i]));
                return *this;
            }

            friend color_quad_u8 operator+(const color_quad_u8 &lhs, const color_quad_u8 &rhs)
            {
                color_quad_u8 result(lhs);
                result += rhs;
                return result;
            }

            friend color_quad_u8 operator-(const color_quad_u8 &lhs, const color_quad_u8 &rhs)
            {
                color_quad_u8 result(lhs);
                result -= rhs;
                return result;
            }
        }; // class color_quad_u8

        struct vec3F
        {
            float m_s[3];

            inline vec3F()
            {
            }
            inline vec3F(float s)
            {
                m_s[0] = s;
                m_s[1] = s;
                m_s[2] = s;
            }
            inline vec3F(float x, float y, float z)
            {
                m_s[0] = x;
                m_s[1] = y;
                m_s[2] = z;
            }

            inline float operator[](uint32_t i) const
            {
                RG_ETC1_ASSERT(i < 3);
                return m_s[i];
            }

            inline vec3F &operator+=(const vec3F &other)
            {
                for (uint32_t i = 0; i < 3; i++)
                    m_s[i] += other.m_s[i];
                return *this;
            }

            inline vec3F &operator*=(float s)
            {
                for (uint32_t i = 0; i < 3; i++)
                    m_s[i] *= s;
                return *this;
            }
        };

        enum etc_constants
        {
            cETC1BytesPerBlock = 8U,
            cETC1SelectorBits = 2U,
            cETC1SelectorValues = 1U << cETC1SelectorBits,
            cETC1SelectorMask = cETC1SelectorValues - 1U,
            cETC1BlockShift = 2U,
            cETC1BlockSize = 1U << cETC1BlockShift,
            cETC1LSBSelectorIndicesBitOffset = 0,
            cETC1MSBSelectorIndicesBitOffset = 16,
            cETC1FlipBitOffset = 32,
            cETC1DiffBitOffset = 33,
            cETC1IntenModifierNumBits = 3,
            cETC1IntenModifierValues = 1 << cETC1IntenModifierNumBits,
            cETC1RightIntenModifierTableBitOffset = 34,
            cETC1LeftIntenModifierTableBitOffset = 37,

            // Base+Delta encoding (5 bit bases, 3 bit delta)
            cETC1BaseColorCompNumBits = 5,
            cETC1BaseColorCompMax = 1 << cETC1BaseColorCompNumBits,
            cETC1DeltaColorCompNumBits = 3,
            cETC1DeltaColorComp = 1 << cETC1DeltaColorCompNumBits,
            cETC1DeltaColorCompMax = 1 << cETC1DeltaColorCompNumBits,
            cETC1BaseColor5RBitOffset = 59,
            cETC1BaseColor5GBitOffset = 51,
            cETC1BaseColor5BBitOffset = 43,
            cETC1DeltaColor3RBitOffset = 56,
            cETC1DeltaColor3GBitOffset = 48,
            cETC1DeltaColor3BBitOffset = 40,

            // Absolute (non-delta) encoding (two 4-bit per component bases)
            cETC1AbsColorCompNumBits = 4,
            cETC1AbsColorCompMax = 1 << cETC1AbsColorCompNumBits,
            cETC1AbsColor4R1BitOffset = 60,
            cETC1AbsColor4G1BitOffset = 52,
            cETC1AbsColor4B1BitOffset = 44,
            cETC1AbsColor4R2BitOffset = 56,
            cETC1AbsColor4G2BitOffset = 48,
            cETC1AbsColor4B2BitOffset = 40,
            cETC1ColorDeltaMin = -4,
            cETC1ColorDeltaMax = 3,

            // Delta3:
            // 0   1   2   3   4   5   6   7
            // 000 001 010 011 100 101 110 111
            // 0   1   2   3   -4  -3  -2  -1
        };

        static uint8_t g_quant5_tab[256 + 16];

        static const int g_etc1_inten_tables[cETC1IntenModifierValues][cETC1SelectorValues] =
            {
                { -8, -2, 2, 8 }, { -17, -5, 5, 17 }, { -29, -9, 9, 29 }, { -42, -13, 13, 42 },
                { -60, -18, 18, 60 }, { -80, -24, 24, 80 }, { -106, -33, 33, 106 }, { -183, -47, 47, 183 }
            };

        static const uint8_t g_etc1_to_selector_index[cETC1SelectorValues] = { 2, 3, 1, 0 };
        static const uint8_t g_selector_index_to_etc1[cETC1SelectorValues] = { 3, 2, 0, 1 };

        // Given an ETC1 diff/inten_table/selector, and an 8-bit desired color, this table encodes the best packed_color in the low byte, and the abs error in the high byte.
        static uint16_t g_etc1_inverse_lookup[2 * 8 * 4][256]; // [diff/inten_table/selector][desired_color]

        // g_color8_to_etc_block_config[color][table_index] = Supplies for each 8-bit color value a list of packed ETC1 diff/intensity table/selectors/packed_colors that map to that color.
        // To pack: diff | (inten << 1) | (selector << 4) | (packed_c << 8)
        static const uint16_t g_color8_to_etc_block_config_0_255[2][33] =
            {
                { 0x0000, 0x0010, 0x0002, 0x0012, 0x0004, 0x0014, 0x0006, 0x0016, 0x0008, 0x0018, 0x000A, 0x001A, 0x000C, 0x001C, 0x000E, 0x001E,
                  0x0001, 0x0011, 0x0003, 0x0013, 0x0005, 0x0015, 0x0007, 0x0017, 0x0009, 0x0019, 0x000B, 0x001B, 0x000D, 0x001D, 0x000F, 0x001F, 0xFFFF },
                { 0x0F20, 0x0F30, 0x0E32, 0x0F22, 0x0E34, 0x0F24, 0x0D36, 0x0F26, 0x0C38, 0x0E28, 0x0B3A, 0x0E2A, 0x093C, 0x0E2C, 0x053E, 0x0D2E,
                  0x1E31, 0x1F21, 0x1D33, 0x1F23, 0x1C35, 0x1E25, 0x1A37, 0x1E27, 0x1839, 0x1D29, 0x163B, 0x1C2B, 0x133D, 0x1B2D, 0x093F, 0x1A2F, 0xFFFF },
            };

        // Really only [254][11].
        static const uint16_t g_color8_to_etc_block_config_1_to_254[254][12] =
            {
                { 0x021C, 0x0D0D, 0xFFFF }, { 0x0020, 0x0021, 0x0A0B, 0x061F, 0xFFFF }, { 0x0113, 0x0217, 0xFFFF }, { 0x0116, 0x031E,
                                                                                                                      0x0B0E, 0x0405, 0xFFFF },
                { 0x0022, 0x0204, 0x050A, 0x0023, 0xFFFF }, { 0x0111, 0x0319, 0x0809, 0x170F, 0xFFFF }, { 0x0303, 0x0215, 0x0607, 0xFFFF }, { 0x0030, 0x0114, 0x0408, 0x0031, 0x0201, 0x051D, 0xFFFF }, { 0x0100, 0x0024, 0x0306,
                                                                                                                                                                                                          0x0025, 0x041B, 0x0E0D, 0xFFFF },
                { 0x021A, 0x0121, 0x0B0B, 0x071F, 0xFFFF }, { 0x0213, 0x0317, 0xFFFF }, { 0x0112,
                                                                                          0x0505, 0xFFFF },
                { 0x0026, 0x070C, 0x0123, 0x0027, 0xFFFF }, { 0x0211, 0x0909, 0xFFFF }, { 0x0110, 0x0315, 0x0707,
                                                                                          0x0419, 0x180F, 0xFFFF },
                { 0x0218, 0x0131, 0x0301, 0x0403, 0x061D, 0xFFFF }, { 0x0032, 0x0202, 0x0033, 0x0125, 0x051B,
                                                                      0x0F0D, 0xFFFF },
                { 0x0028, 0x031C, 0x0221, 0x0029, 0xFFFF }, { 0x0120, 0x0313, 0x0C0B, 0x081F, 0xFFFF }, { 0x0605,
                                                                                                          0x0417, 0xFFFF },
                { 0x0216, 0x041E, 0x0C0E, 0x0223, 0x0127, 0xFFFF }, { 0x0122, 0x0304, 0x060A, 0x0311, 0x0A09, 0xFFFF }, { 0x0519, 0x190F, 0xFFFF }, { 0x002A, 0x0231, 0x0503, 0x0415, 0x0807, 0x002B, 0x071D, 0xFFFF }, { 0x0130, 0x0214,
                                                                                                                                                                                                                          0x0508, 0x0401, 0x0133, 0x0225, 0x061B, 0xFFFF },
                { 0x0200, 0x0124, 0x0406, 0x0321, 0x0129, 0x100D, 0xFFFF }, { 0x031A,
                                                                              0x0D0B, 0x091F, 0xFFFF },
                { 0x0413, 0x0705, 0x0517, 0xFFFF }, { 0x0212, 0x0034, 0x0323, 0x0035, 0x0227, 0xFFFF }, { 0x0126, 0x080C, 0x0B09, 0xFFFF }, { 0x0411, 0x0619, 0x1A0F, 0xFFFF }, { 0x0210, 0x0331, 0x0603, 0x0515, 0x0907, 0x012B,
                                                                                                                                                                                  0xFFFF },
                { 0x0318, 0x002C, 0x0501, 0x0233, 0x0325, 0x071B, 0x002D, 0x081D, 0xFFFF }, { 0x0132, 0x0302, 0x0229, 0x110D,
                                                                                              0xFFFF },
                { 0x0128, 0x041C, 0x0421, 0x0E0B, 0x0A1F, 0xFFFF }, { 0x0220, 0x0513, 0x0617, 0xFFFF }, { 0x0135, 0x0805,
                                                                                                          0x0327, 0xFFFF },
                { 0x0316, 0x051E, 0x0D0E, 0x0423, 0xFFFF }, { 0x0222, 0x0404, 0x070A, 0x0511, 0x0719, 0x0C09, 0x1B0F,
                                                              0xFFFF },
                { 0x0703, 0x0615, 0x0A07, 0x022B, 0xFFFF }, { 0x012A, 0x0431, 0x0601, 0x0333, 0x012D, 0x091D, 0xFFFF }, { 0x0230, 0x0314, 0x0036, 0x0608, 0x0425, 0x0037, 0x0329, 0x081B, 0x120D, 0xFFFF }, { 0x0300, 0x0224, 0x0506, 0x0521,
                                                                                                                                                                                                              0x0F0B, 0x0B1F, 0xFFFF },
                { 0x041A, 0x0613, 0x0717, 0xFFFF }, { 0x0235, 0x0905, 0xFFFF }, { 0x0312, 0x0134, 0x0523,
                                                                                  0x0427, 0xFFFF },
                { 0x0226, 0x090C, 0x002E, 0x0611, 0x0D09, 0x002F, 0xFFFF }, { 0x0715, 0x0B07, 0x0819, 0x032B, 0x1C0F,
                                                                              0xFFFF },
                { 0x0310, 0x0531, 0x0701, 0x0803, 0x022D, 0x0A1D, 0xFFFF }, { 0x0418, 0x012C, 0x0433, 0x0525, 0x0137, 0x091B,
                                                                              0x130D, 0xFFFF },
                { 0x0232, 0x0402, 0x0621, 0x0429, 0xFFFF }, { 0x0228, 0x051C, 0x0713, 0x100B, 0x0C1F, 0xFFFF }, { 0x0320, 0x0335, 0x0A05, 0x0817, 0xFFFF }, { 0x0623, 0x0527, 0xFFFF }, { 0x0416, 0x061E, 0x0E0E, 0x0711, 0x0E09, 0x012F,
                                                                                                                                                                                          0xFFFF },
                { 0x0322, 0x0504, 0x080A, 0x0919, 0x1D0F, 0xFFFF }, { 0x0631, 0x0903, 0x0815, 0x0C07, 0x042B, 0x032D, 0x0B1D,
                                                                      0xFFFF },
                { 0x022A, 0x0801, 0x0533, 0x0625, 0x0237, 0x0A1B, 0xFFFF }, { 0x0330, 0x0414, 0x0136, 0x0708, 0x0721, 0x0529,
                                                                              0x140D, 0xFFFF },
                { 0x0400, 0x0324, 0x0606, 0x0038, 0x0039, 0x110B, 0x0D1F, 0xFFFF }, { 0x051A, 0x0813, 0x0B05, 0x0917,
                                                                                      0xFFFF },
                { 0x0723, 0x0435, 0x0627, 0xFFFF }, { 0x0412, 0x0234, 0x0F09, 0x022F, 0xFFFF }, { 0x0326, 0x0A0C, 0x012E,
                                                                                                  0x0811, 0x0A19, 0x1E0F, 0xFFFF },
                { 0x0731, 0x0A03, 0x0915, 0x0D07, 0x052B, 0xFFFF }, { 0x0410, 0x0901, 0x0633, 0x0725,
                                                                      0x0337, 0x0B1B, 0x042D, 0x0C1D, 0xFFFF },
                { 0x0518, 0x022C, 0x0629, 0x150D, 0xFFFF }, { 0x0332, 0x0502, 0x0821, 0x0139,
                                                              0x120B, 0x0E1F, 0xFFFF },
                { 0x0328, 0x061C, 0x0913, 0x0A17, 0xFFFF }, { 0x0420, 0x0535, 0x0C05, 0x0727, 0xFFFF }, { 0x0823, 0x032F, 0xFFFF }, { 0x0516, 0x071E, 0x0F0E, 0x0911, 0x0B19, 0x1009, 0x1F0F, 0xFFFF }, { 0x0422, 0x0604, 0x090A,
                                                                                                                                                                                                          0x0B03, 0x0A15, 0x0E07, 0x062B, 0xFFFF },
                { 0x0831, 0x0A01, 0x0733, 0x052D, 0x0D1D, 0xFFFF }, { 0x032A, 0x0825, 0x0437,
                                                                      0x0729, 0x0C1B, 0x160D, 0xFFFF },
                { 0x0430, 0x0514, 0x0236, 0x0808, 0x0921, 0x0239, 0x130B, 0x0F1F, 0xFFFF }, { 0x0500,
                                                                                              0x0424, 0x0706, 0x0138, 0x0A13, 0x0B17, 0xFFFF },
                { 0x061A, 0x0635, 0x0D05, 0xFFFF }, { 0x0923, 0x0827, 0xFFFF }, { 0x0512, 0x0334, 0x003A, 0x0A11, 0x1109, 0x003B, 0x042F, 0xFFFF }, { 0x0426, 0x0B0C, 0x022E, 0x0B15, 0x0F07, 0x0C19,
                                                                                                                                                      0x072B, 0xFFFF },
                { 0x0931, 0x0B01, 0x0C03, 0x062D, 0x0E1D, 0xFFFF }, { 0x0510, 0x0833, 0x0925, 0x0537, 0x0D1B, 0x170D,
                                                                      0xFFFF },
                { 0x0618, 0x032C, 0x0A21, 0x0339, 0x0829, 0xFFFF }, { 0x0432, 0x0602, 0x0B13, 0x140B, 0x101F, 0xFFFF }, { 0x0428, 0x071C, 0x0735, 0x0E05, 0x0C17, 0xFFFF }, { 0x0520, 0x0A23, 0x0927, 0xFFFF }, { 0x0B11, 0x1209, 0x013B, 0x052F,
                                                                                                                                                                                                                  0xFFFF },
                { 0x0616, 0x081E, 0x0D19, 0xFFFF }, { 0x0522, 0x0704, 0x0A0A, 0x0A31, 0x0D03, 0x0C15, 0x1007, 0x082B, 0x072D,
                                                      0x0F1D, 0xFFFF },
                { 0x0C01, 0x0933, 0x0A25, 0x0637, 0x0E1B, 0xFFFF }, { 0x042A, 0x0B21, 0x0929, 0x180D, 0xFFFF }, { 0x0530, 0x0614, 0x0336, 0x0908, 0x0439, 0x150B, 0x111F, 0xFFFF }, { 0x0600, 0x0524, 0x0806, 0x0238, 0x0C13, 0x0F05,
                                                                                                                                                                                      0x0D17, 0xFFFF },
                { 0x071A, 0x0B23, 0x0835, 0x0A27, 0xFFFF }, { 0x1309, 0x023B, 0x062F, 0xFFFF }, { 0x0612, 0x0434,
                                                                                                  0x013A, 0x0C11, 0x0E19, 0xFFFF },
                { 0x0526, 0x0C0C, 0x032E, 0x0B31, 0x0E03, 0x0D15, 0x1107, 0x092B, 0xFFFF }, { 0x0D01,
                                                                                              0x0A33, 0x0B25, 0x0737, 0x0F1B, 0x082D, 0x101D, 0xFFFF },
                { 0x0610, 0x0A29, 0x190D, 0xFFFF }, { 0x0718, 0x042C, 0x0C21,
                                                      0x0539, 0x160B, 0x121F, 0xFFFF },
                { 0x0532, 0x0702, 0x0D13, 0x0E17, 0xFFFF }, { 0x0528, 0x081C, 0x0935, 0x1005, 0x0B27,
                                                              0xFFFF },
                { 0x0620, 0x0C23, 0x033B, 0x072F, 0xFFFF }, { 0x0D11, 0x0F19, 0x1409, 0xFFFF }, { 0x0716, 0x003C, 0x091E,
                                                                                                  0x0F03, 0x0E15, 0x1207, 0x0A2B, 0x003D, 0xFFFF },
                { 0x0622, 0x0804, 0x0B0A, 0x0C31, 0x0E01, 0x0B33, 0x092D, 0x111D,
                  0xFFFF },
                { 0x0C25, 0x0837, 0x0B29, 0x101B, 0x1A0D, 0xFFFF }, { 0x052A, 0x0D21, 0x0639, 0x170B, 0x131F, 0xFFFF }, { 0x0630, 0x0714, 0x0436, 0x0A08, 0x0E13, 0x0F17, 0xFFFF }, { 0x0700, 0x0624, 0x0906, 0x0338, 0x0A35, 0x1105, 0xFFFF }, { 0x081A, 0x0D23, 0x0C27, 0xFFFF }, { 0x0E11, 0x1509, 0x043B, 0x082F, 0xFFFF }, { 0x0712, 0x0534, 0x023A, 0x0F15, 0x1307,
                                                                                                                                                                                                                                                                                                                                  0x1019, 0x0B2B, 0x013D, 0xFFFF },
                { 0x0626, 0x0D0C, 0x042E, 0x0D31, 0x0F01, 0x1003, 0x0A2D, 0x121D, 0xFFFF }, { 0x0C33,
                                                                                              0x0D25, 0x0937, 0x111B, 0x1B0D, 0xFFFF },
                { 0x0710, 0x0E21, 0x0739, 0x0C29, 0xFFFF }, { 0x0818, 0x052C, 0x0F13, 0x180B,
                                                              0x141F, 0xFFFF },
                { 0x0632, 0x0802, 0x0B35, 0x1205, 0x1017, 0xFFFF }, { 0x0628, 0x091C, 0x0E23, 0x0D27, 0xFFFF }, { 0x0720, 0x0F11, 0x1609, 0x053B, 0x092F, 0xFFFF }, { 0x1119, 0x023D, 0xFFFF }, { 0x0816, 0x013C, 0x0A1E, 0x0E31, 0x1103,
                                                                                                                                                                                                  0x1015, 0x1407, 0x0C2B, 0x0B2D, 0x131D, 0xFFFF },
                { 0x0722, 0x0904, 0x0C0A, 0x1001, 0x0D33, 0x0E25, 0x0A37, 0x121B,
                  0xFFFF },
                { 0x0F21, 0x0D29, 0x1C0D, 0xFFFF }, { 0x062A, 0x0839, 0x190B, 0x151F, 0xFFFF }, { 0x0730, 0x0814, 0x0536,
                                                                                                  0x0B08, 0x1013, 0x1305, 0x1117, 0xFFFF },
                { 0x0800, 0x0724, 0x0A06, 0x0438, 0x0F23, 0x0C35, 0x0E27, 0xFFFF }, { 0x091A,
                                                                                      0x1709, 0x063B, 0x0A2F, 0xFFFF },
                { 0x1011, 0x1219, 0x033D, 0xFFFF }, { 0x0812, 0x0634, 0x033A, 0x0F31, 0x1203, 0x1115,
                                                      0x1507, 0x0D2B, 0xFFFF },
                { 0x0726, 0x0E0C, 0x052E, 0x1101, 0x0E33, 0x0F25, 0x0B37, 0x131B, 0x0C2D, 0x141D, 0xFFFF }, { 0x0E29, 0x1D0D, 0xFFFF }, { 0x0810, 0x1021, 0x0939, 0x1A0B, 0x161F, 0xFFFF }, { 0x0918, 0x062C, 0x1113, 0x1217, 0xFFFF }, { 0x0732, 0x0902, 0x0D35, 0x1405, 0x0F27, 0xFFFF }, { 0x0728, 0x0A1C, 0x1023, 0x073B, 0x0B2F, 0xFFFF }, { 0x0820,
                                                                                                                                                                                                                                                                                                                                                  0x1111, 0x1319, 0x1809, 0xFFFF },
                { 0x1303, 0x1215, 0x1607, 0x0E2B, 0x043D, 0xFFFF }, { 0x0916, 0x023C, 0x0B1E, 0x1031,
                                                                      0x1201, 0x0F33, 0x0D2D, 0x151D, 0xFFFF },
                { 0x0822, 0x0A04, 0x0D0A, 0x1025, 0x0C37, 0x0F29, 0x141B, 0x1E0D, 0xFFFF }, { 0x1121, 0x0A39, 0x1B0B, 0x171F, 0xFFFF }, { 0x072A, 0x1213, 0x1317, 0xFFFF }, { 0x0830, 0x0914, 0x0636, 0x0C08, 0x0E35,
                                                                                                                                                                              0x1505, 0xFFFF },
                { 0x0900, 0x0824, 0x0B06, 0x0538, 0x1123, 0x1027, 0xFFFF }, { 0x0A1A, 0x1211, 0x1909, 0x083B, 0x0C2F,
                                                                              0xFFFF },
                { 0x1315, 0x1707, 0x1419, 0x0F2B, 0x053D, 0xFFFF }, { 0x0912, 0x0734, 0x043A, 0x1131, 0x1301, 0x1403, 0x0E2D,
                                                                      0x161D, 0xFFFF },
                { 0x0826, 0x0F0C, 0x062E, 0x1033, 0x1125, 0x0D37, 0x151B, 0x1F0D, 0xFFFF }, { 0x1221, 0x0B39, 0x1029,
                                                                                              0xFFFF },
                { 0x0910, 0x1313, 0x1C0B, 0x181F, 0xFFFF }, { 0x0A18, 0x072C, 0x0F35, 0x1605, 0x1417, 0xFFFF }, { 0x0832,
                                                                                                                  0x0A02, 0x1223, 0x1127, 0xFFFF },
                { 0x0828, 0x0B1C, 0x1311, 0x1A09, 0x093B, 0x0D2F, 0xFFFF }, { 0x0920, 0x1519, 0x063D,
                                                                              0xFFFF },
                { 0x1231, 0x1503, 0x1415, 0x1807, 0x102B, 0x0F2D, 0x171D, 0xFFFF }, { 0x0A16, 0x033C, 0x0C1E, 0x1401, 0x1133,
                                                                                      0x1225, 0x0E37, 0x161B, 0xFFFF },
                { 0x0922, 0x0B04, 0x0E0A, 0x1321, 0x1129, 0xFFFF }, { 0x0C39, 0x1D0B, 0x191F, 0xFFFF }, { 0x082A, 0x1413, 0x1705, 0x1517, 0xFFFF }, { 0x0930, 0x0A14, 0x0736, 0x0D08, 0x1323, 0x1035, 0x1227, 0xFFFF }, { 0x0A00, 0x0924, 0x0C06, 0x0638, 0x1B09, 0x0A3B, 0x0E2F, 0xFFFF }, { 0x0B1A, 0x1411, 0x1619, 0x073D, 0xFFFF }, { 0x1331,
                                                                                                                                                                                                                                                                                                                                          0x1603, 0x1515, 0x1907, 0x112B, 0xFFFF },
                { 0x0A12, 0x0834, 0x053A, 0x1501, 0x1233, 0x1325, 0x0F37, 0x171B, 0x102D,
                  0x181D, 0xFFFF },
                { 0x0926, 0x072E, 0x1229, 0xFFFF }, { 0x1421, 0x0D39, 0x1E0B, 0x1A1F, 0xFFFF }, { 0x0A10, 0x1513,
                                                                                                  0x1617, 0xFFFF },
                { 0x0B18, 0x082C, 0x1135, 0x1805, 0x1327, 0xFFFF }, { 0x0932, 0x0B02, 0x1423, 0x0B3B, 0x0F2F, 0xFFFF }, { 0x0928, 0x0C1C, 0x1511, 0x1719, 0x1C09, 0xFFFF }, { 0x0A20, 0x1703, 0x1615, 0x1A07, 0x122B, 0x083D, 0xFFFF }, { 0x1431, 0x1601, 0x1333, 0x112D, 0x191D, 0xFFFF }, { 0x0B16, 0x043C, 0x0D1E, 0x1425, 0x1037, 0x1329, 0x181B, 0xFFFF }, { 0x0A22, 0x0C04, 0x0F0A, 0x1521, 0x0E39, 0x1F0B, 0x1B1F, 0xFFFF }, { 0x1613, 0x1717, 0xFFFF }, { 0x092A, 0x1235, 0x1905,
                                                                                                                                                                                                                                                                                                                                                                                                                                                                  0xFFFF },
                { 0x0A30, 0x0B14, 0x0836, 0x0E08, 0x1523, 0x1427, 0xFFFF }, { 0x0B00, 0x0A24, 0x0D06, 0x0738, 0x1611, 0x1D09,
                                                                              0x0C3B, 0x102F, 0xFFFF },
                { 0x0C1A, 0x1715, 0x1B07, 0x1819, 0x132B, 0x093D, 0xFFFF }, { 0x1531, 0x1701, 0x1803, 0x122D,
                                                                              0x1A1D, 0xFFFF },
                { 0x0B12, 0x0934, 0x063A, 0x1433, 0x1525, 0x1137, 0x191B, 0xFFFF }, { 0x0A26, 0x003E, 0x082E, 0x1621,
                                                                                      0x0F39, 0x1429, 0x003F, 0xFFFF },
                { 0x1713, 0x1C1F, 0xFFFF }, { 0x0B10, 0x1335, 0x1A05, 0x1817, 0xFFFF }, { 0x0C18,
                                                                                          0x092C, 0x1623, 0x1527, 0xFFFF },
                { 0x0A32, 0x0C02, 0x1711, 0x1E09, 0x0D3B, 0x112F, 0xFFFF }, { 0x0A28, 0x0D1C, 0x1919,
                                                                              0x0A3D, 0xFFFF },
                { 0x0B20, 0x1631, 0x1903, 0x1815, 0x1C07, 0x142B, 0x132D, 0x1B1D, 0xFFFF }, { 0x1801, 0x1533, 0x1625,
                                                                                              0x1237, 0x1A1B, 0xFFFF },
                { 0x0C16, 0x053C, 0x0E1E, 0x1721, 0x1529, 0x013F, 0xFFFF }, { 0x0B22, 0x0D04, 0x1039, 0x1D1F,
                                                                              0xFFFF },
                { 0x1813, 0x1B05, 0x1917, 0xFFFF }, { 0x0A2A, 0x1723, 0x1435, 0x1627, 0xFFFF }, { 0x0B30, 0x0C14, 0x0936,
                                                                                                  0x0F08, 0x1F09, 0x0E3B, 0x122F, 0xFFFF },
                { 0x0C00, 0x0B24, 0x0E06, 0x0838, 0x1811, 0x1A19, 0x0B3D, 0xFFFF }, { 0x0D1A,
                                                                                      0x1731, 0x1A03, 0x1915, 0x1D07, 0x152B, 0xFFFF },
                { 0x1901, 0x1633, 0x1725, 0x1337, 0x1B1B, 0x142D, 0x1C1D, 0xFFFF }, { 0x0C12, 0x0A34, 0x073A, 0x1629, 0x023F, 0xFFFF }, { 0x0B26, 0x013E, 0x092E, 0x1821, 0x1139, 0x1E1F, 0xFFFF }, { 0x1913,
                                                                                                                                                                                                      0x1A17, 0xFFFF },
                { 0x0C10, 0x1535, 0x1C05, 0x1727, 0xFFFF }, { 0x0D18, 0x0A2C, 0x1823, 0x0F3B, 0x132F, 0xFFFF }, { 0x0B32, 0x0D02, 0x1911, 0x1B19, 0xFFFF }, { 0x0B28, 0x0E1C, 0x1B03, 0x1A15, 0x1E07, 0x162B, 0x0C3D, 0xFFFF }, { 0x0C20,
                                                                                                                                                                                                                                  0x1831, 0x1A01, 0x1733, 0x152D, 0x1D1D, 0xFFFF },
                { 0x1825, 0x1437, 0x1729, 0x1C1B, 0x033F, 0xFFFF }, { 0x0D16, 0x063C,
                                                                      0x0F1E, 0x1921, 0x1239, 0x1F1F, 0xFFFF },
                { 0x0C22, 0x0E04, 0x1A13, 0x1B17, 0xFFFF }, { 0x1635, 0x1D05, 0xFFFF }, { 0x0B2A, 0x1923, 0x1827, 0xFFFF }, { 0x0C30, 0x0D14, 0x0A36, 0x1A11, 0x103B, 0x142F, 0xFFFF }, { 0x0D00, 0x0C24, 0x0F06,
                                                                                                                                                                                          0x0938, 0x1B15, 0x1F07, 0x1C19, 0x172B, 0x0D3D, 0xFFFF },
                { 0x0E1A, 0x1931, 0x1B01, 0x1C03, 0x162D, 0x1E1D, 0xFFFF }, { 0x1833, 0x1925, 0x1537, 0x1D1B, 0xFFFF }, { 0x0D12, 0x0B34, 0x083A, 0x1A21, 0x1339, 0x1829, 0x043F, 0xFFFF }, { 0x0C26,
                                                                                                                                                                                              0x023E, 0x0A2E, 0x1B13, 0xFFFF },
                { 0x1735, 0x1E05, 0x1C17, 0xFFFF }, { 0x0D10, 0x1A23, 0x1927, 0xFFFF }, { 0x0E18,
                                                                                          0x0B2C, 0x1B11, 0x113B, 0x152F, 0xFFFF },
                { 0x0C32, 0x0E02, 0x1D19, 0x0E3D, 0xFFFF }, { 0x0C28, 0x0F1C, 0x1A31, 0x1D03,
                                                              0x1C15, 0x182B, 0x172D, 0x1F1D, 0xFFFF },
                { 0x0D20, 0x1C01, 0x1933, 0x1A25, 0x1637, 0x1E1B, 0xFFFF }, { 0x1B21, 0x1929,
                                                                              0x053F, 0xFFFF },
                { 0x0E16, 0x073C, 0x1439, 0xFFFF }, { 0x0D22, 0x0F04, 0x1C13, 0x1F05, 0x1D17, 0xFFFF }, { 0x1B23,
                                                                                                          0x1835, 0x1A27, 0xFFFF },
                { 0x0C2A, 0x123B, 0x162F, 0xFFFF }, { 0x0D30, 0x0E14, 0x0B36, 0x1C11, 0x1E19, 0x0F3D, 0xFFFF }, { 0x0E00, 0x0D24, 0x0A38, 0x1B31, 0x1E03, 0x1D15, 0x192B, 0xFFFF }, { 0x0F1A, 0x1D01, 0x1A33, 0x1B25, 0x1737, 0x1F1B,
                                                                                                                                                                                      0x182D, 0xFFFF },
                { 0x1A29, 0x063F, 0xFFFF }, { 0x0E12, 0x0C34, 0x093A, 0x1C21, 0x1539, 0xFFFF }, { 0x0D26, 0x033E,
                                                                                                  0x0B2E, 0x1D13, 0x1E17, 0xFFFF },
                { 0x1935, 0x1B27, 0xFFFF }, { 0x0E10, 0x1C23, 0x133B, 0x172F, 0xFFFF }, { 0x0F18,
                                                                                          0x0C2C, 0x1D11, 0x1F19, 0xFFFF },
                { 0x0D32, 0x0F02, 0x1F03, 0x1E15, 0x1A2B, 0x103D, 0xFFFF }, { 0x0D28, 0x1C31, 0x1E01,
                                                                              0x1B33, 0x192D, 0xFFFF },
                { 0x0E20, 0x1C25, 0x1837, 0x1B29, 0x073F, 0xFFFF }, { 0x1D21, 0x1639, 0xFFFF }, { 0x0F16,
                                                                                                  0x083C, 0x1E13, 0x1F17, 0xFFFF },
                { 0x0E22, 0x1A35, 0xFFFF }, { 0x1D23, 0x1C27, 0xFFFF }, { 0x0D2A, 0x1E11, 0x143B,
                                                                          0x182F, 0xFFFF },
                { 0x0E30, 0x0F14, 0x0C36, 0x1F15, 0x1B2B, 0x113D, 0xFFFF }, { 0x0F00, 0x0E24, 0x0B38, 0x1D31, 0x1F01,
                                                                              0x1A2D, 0xFFFF },
                { 0x1C33, 0x1D25, 0x1937, 0xFFFF }, { 0x1E21, 0x1739, 0x1C29, 0x083F, 0xFFFF }, { 0x0F12, 0x0D34,
                                                                                                  0x0A3A, 0x1F13, 0xFFFF },
                { 0x0E26, 0x043E, 0x0C2E, 0x1B35, 0xFFFF }, { 0x1E23, 0x1D27, 0xFFFF }, { 0x0F10, 0x1F11,
                                                                                          0x153B, 0x192F, 0xFFFF },
                { 0x0D2C, 0x123D, 0xFFFF },
            };

        struct etc1_block
        {
            // big endian uint64_t:
            // bit ofs:  56  48  40  32  24  16   8   0
            // byte ofs: b0, b1, b2, b3, b4, b5, b6, b7
            union
            {
                uint64_t m_uint64;
                uint8_t m_bytes[8];
            };

            uint8_t m_low_color[2];
            uint8_t m_high_color[2];

            enum
            {
                cNumSelectorBytes = 4
            };
            uint8_t m_selectors[cNumSelectorBytes];

            inline void clear()
            {
                zero_this(this);
            }

            inline uint32_t get_byte_bits(uint32_t ofs, uint32_t num) const
            {
                RG_ETC1_ASSERT((ofs + num) <= 64U);
                RG_ETC1_ASSERT(num && (num <= 8U));
                RG_ETC1_ASSERT((ofs >> 3) == ((ofs + num - 1) >> 3));
                const uint32_t byte_ofs = 7 - (ofs >> 3);
                const uint32_t byte_bit_ofs = ofs & 7;
                return (m_bytes[byte_ofs] >> byte_bit_ofs) & ((1 << num) - 1);
            }

            inline void set_byte_bits(uint32_t ofs, uint32_t num, uint32_t bits)
            {
                RG_ETC1_ASSERT((ofs + num) <= 64U);
                RG_ETC1_ASSERT(num && (num < 32U));
                RG_ETC1_ASSERT((ofs >> 3) == ((ofs + num - 1) >> 3));
                RG_ETC1_ASSERT(bits < (1U << num));
                const uint32_t byte_ofs = 7 - (ofs >> 3);
                const uint32_t byte_bit_ofs = ofs & 7;
                const uint32_t mask = (1 << num) - 1;
                m_bytes[byte_ofs] &= ~(mask << byte_bit_ofs);
                m_bytes[byte_ofs] |= (bits << byte_bit_ofs);
            }

            // false = left/right subblocks
            // true = upper/lower subblocks
            inline bool get_flip_bit() const
            {
                return (m_bytes[3] & 1) != 0;
            }

            inline void set_flip_bit(bool flip)
            {
                m_bytes[3] &= ~1;
                m_bytes[3] |= static_cast<uint8_t>(flip);
            }

            inline bool get_diff_bit() const
            {
                return (m_bytes[3] & 2) != 0;
            }

            inline void set_diff_bit(bool diff)
            {
                m_bytes[3] &= ~2;
                m_bytes[3] |= (static_cast<uint32_t>(diff) << 1);
            }

            // Returns intensity modifier table (0-7) used by subblock subblock_id.
            // subblock_id=0 left/top (CW 1), 1=right/bottom (CW 2)
            inline uint32_t get_inten_table(uint32_t subblock_id) const
            {
                RG_ETC1_ASSERT(subblock_id < 2);
                const uint32_t ofs = subblock_id ? 2 : 5;
                return (m_bytes[3] >> ofs) & 7;
            }

            // Sets intensity modifier table (0-7) used by subblock subblock_id (0 or 1)
            inline void set_inten_table(uint32_t subblock_id, uint32_t t)
            {
                RG_ETC1_ASSERT(subblock_id < 2);
                RG_ETC1_ASSERT(t < 8);
                const uint32_t ofs = subblock_id ? 2 : 5;
                m_bytes[3] &= ~(7 << ofs);
                m_bytes[3] |= (t << ofs);
            }

            // Returned selector value ranges from 0-3 and is a direct index into g_etc1_inten_tables.
            inline uint32_t get_selector(uint32_t x, uint32_t y) const
            {
                RG_ETC1_ASSERT((x | y) < 4);

                const uint32_t bit_index = x * 4 + y;
                const uint32_t byte_bit_ofs = bit_index & 7;
                const uint8_t *p = &m_bytes[7 - (bit_index >> 3)];
                const uint32_t lsb = (p[0] >> byte_bit_ofs) & 1;
                const uint32_t msb = (p[-2] >> byte_bit_ofs) & 1;
                const uint32_t val = lsb | (msb << 1);

                return g_etc1_to_selector_index[val];
            }

            // Selector "val" ranges from 0-3 and is a direct index into g_etc1_inten_tables.
            inline void set_selector(uint32_t x, uint32_t y, uint32_t val)
            {
                RG_ETC1_ASSERT((x | y | val) < 4);
                const uint32_t bit_index = x * 4 + y;

                uint8_t *p = &m_bytes[7 - (bit_index >> 3)];

                const uint32_t byte_bit_ofs = bit_index & 7;
                const uint32_t mask = 1 << byte_bit_ofs;

                const uint32_t etc1_val = g_selector_index_to_etc1[val];

                const uint32_t lsb = etc1_val & 1;
                const uint32_t msb = etc1_val >> 1;

                p[0] &= ~mask;
                p[0] |= (lsb << byte_bit_ofs);

                p[-2] &= ~mask;
                p[-2] |= (msb << byte_bit_ofs);
            }

            inline void set_base4_color(uint32_t idx, uint16_t c)
            {
                if (idx)
                {
                    set_byte_bits(cETC1AbsColor4R2BitOffset, 4, (c >> 8) & 15);
                    set_byte_bits(cETC1AbsColor4G2BitOffset, 4, (c >> 4) & 15);
                    set_byte_bits(cETC1AbsColor4B2BitOffset, 4, c & 15);
                }
                else
                {
                    set_byte_bits(cETC1AbsColor4R1BitOffset, 4, (c >> 8) & 15);
                    set_byte_bits(cETC1AbsColor4G1BitOffset, 4, (c >> 4) & 15);
                    set_byte_bits(cETC1AbsColor4B1BitOffset, 4, c & 15);
                }
            }

            inline uint16_t get_base4_color(uint32_t idx) const
            {
                uint32_t r, g, b;
                if (idx)
                {
                    r = get_byte_bits(cETC1AbsColor4R2BitOffset, 4);
                    g = get_byte_bits(cETC1AbsColor4G2BitOffset, 4);
                    b = get_byte_bits(cETC1AbsColor4B2BitOffset, 4);
                }
                else
                {
                    r = get_byte_bits(cETC1AbsColor4R1BitOffset, 4);
                    g = get_byte_bits(cETC1AbsColor4G1BitOffset, 4);
                    b = get_byte_bits(cETC1AbsColor4B1BitOffset, 4);
                }
                return static_cast<uint16_t>(b | (g << 4U) | (r << 8U));
            }

            inline void set_base5_color(uint16_t c)
            {
                set_byte_bits(cETC1BaseColor5RBitOffset, 5, (c >> 10) & 31);
                set_byte_bits(cETC1BaseColor5GBitOffset, 5, (c >> 5) & 31);
                set_byte_bits(cETC1BaseColor5BBitOffset, 5, c & 31);
            }

            inline uint16_t get_base5_color() const
            {
                const uint32_t r = get_byte_bits(cETC1BaseColor5RBitOffset, 5);
                const uint32_t g = get_byte_bits(cETC1BaseColor5GBitOffset, 5);
                const uint32_t b = get_byte_bits(cETC1BaseColor5BBitOffset, 5);
                return static_cast<uint16_t>(b | (g << 5U) | (r << 10U));
            }

            void set_delta3_color(uint16_t c)
            {
                set_byte_bits(cETC1DeltaColor3RBitOffset, 3, (c >> 6) & 7);
                set_byte_bits(cETC1DeltaColor3GBitOffset, 3, (c >> 3) & 7);
                set_byte_bits(cETC1DeltaColor3BBitOffset, 3, c & 7);
            }

            inline uint16_t get_delta3_color() const
            {
                const uint32_t r = get_byte_bits(cETC1DeltaColor3RBitOffset, 3);
                const uint32_t g = get_byte_bits(cETC1DeltaColor3GBitOffset, 3);
                const uint32_t b = get_byte_bits(cETC1DeltaColor3BBitOffset, 3);
                return static_cast<uint16_t>(b | (g << 3U) | (r << 6U));
            }

            // Base color 5
            static uint16_t pack_color5(const color_quad_u8 &color, bool scaled, uint32_t bias = 127U);
            static uint16_t pack_color5(uint32_t r, uint32_t g, uint32_t b, bool scaled, uint32_t bias = 127U);

            static color_quad_u8 unpack_color5(uint16_t packed_color5, bool scaled, uint32_t alpha = 255U);
            static void unpack_color5(uint32_t &r, uint32_t &g, uint32_t &b, uint16_t packed_color, bool scaled);

            static bool unpack_color5(color_quad_u8 &result, uint16_t packed_color5, uint16_t packed_delta3, bool scaled, uint32_t alpha = 255U);
            static bool unpack_color5(uint32_t &r, uint32_t &g, uint32_t &b, uint16_t packed_color5, uint16_t packed_delta3, bool scaled, uint32_t alpha = 255U);

            // Delta color 3
            // Inputs range from -4 to 3 (cETC1ColorDeltaMin to cETC1ColorDeltaMax)
            static uint16_t pack_delta3(int r, int g, int b);

            // Results range from -4 to 3 (cETC1ColorDeltaMin to cETC1ColorDeltaMax)
            static void unpack_delta3(int &r, int &g, int &b, uint16_t packed_delta3);

            // Abs color 4
            static uint16_t pack_color4(const color_quad_u8 &color, bool scaled, uint32_t bias = 127U);
            static uint16_t pack_color4(uint32_t r, uint32_t g, uint32_t b, bool scaled, uint32_t bias = 127U);

            static color_quad_u8 unpack_color4(uint16_t packed_color4, bool scaled, uint32_t alpha = 255U);
            static void unpack_color4(uint32_t &r, uint32_t &g, uint32_t &b, uint16_t packed_color4, bool scaled);

            // subblock colors
            static void get_diff_subblock_colors(color_quad_u8 *pDst, uint16_t packed_color5, uint32_t table_idx);
            static bool get_diff_subblock_colors(color_quad_u8 *pDst, uint16_t packed_color5, uint16_t packed_delta3, uint32_t table_idx);
            static void get_abs_subblock_colors(color_quad_u8 *pDst, uint16_t packed_color4, uint32_t table_idx);

            static inline void unscaled_to_scaled_color(color_quad_u8 &dst, const color_quad_u8 &src, bool color4)
            {
                if (color4)
                {
                    dst.r = src.r | (src.r << 4);
                    dst.g = src.g | (src.g << 4);
                    dst.b = src.b | (src.b << 4);
                }
                else
                {
                    dst.r = (src.r >> 2) | (src.r << 3);
                    dst.g = (src.g >> 2) | (src.g << 3);
                    dst.b = (src.b >> 2) | (src.b << 3);
                }
                dst.a = src.a;
            }
        };

        // Returns pointer to sorted array.
        template <typename T, typename Q>
        T *indirect_radix_sort(uint32_t num_indices, T *pIndices0, T *pIndices1, const Q *pKeys, uint32_t key_ofs, uint32_t key_size, bool init_indices)
        {
            //RG_ETC1_ASSERT((key_ofs >= 0) && (key_ofs < sizeof(T)));
            RG_ETC1_ASSERT(key_ofs < sizeof(T));
            RG_ETC1_ASSERT((key_size >= 1) && (key_size <= 4));

            if (init_indices)
            {
                T *p = pIndices0;
                T *q = pIndices0 + (num_indices >> 1) * 2;
                uint32_t i;
                for (i = 0; p != q; p += 2, i += 2)
                {
                    p[0] = static_cast<T>(i);
                    p[1] = static_cast<T>(i + 1);
                }

                if (num_indices & 1)
                    *p = static_cast<T>(i);
            }

            uint32_t hist[256 * 4];

            memset(hist, 0, sizeof(hist[0]) * 256 * key_size);

#define RG_ETC1_GET_KEY(p) (*(const uint32_t *)((const uint8_t *)(pKeys + *(p)) + key_ofs))
#define RG_ETC1_GET_KEY_FROM_INDEX(i) (*(const uint32_t *)((const uint8_t *)(pKeys + (i)) + key_ofs))

            if (key_size == 4)
            {
                T *p = pIndices0;
                T *q = pIndices0 + num_indices;
                for (; p != q; p++)
                {
                    const uint32_t key = RG_ETC1_GET_KEY(p);

                    hist[key & 0xFF]++;
                    hist[256 + ((key >> 8) & 0xFF)]++;
                    hist[512 + ((key >> 16) & 0xFF)]++;
                    hist[768 + ((key >> 24) & 0xFF)]++;
                }
            }
            else if (key_size == 3)
            {
                T *p = pIndices0;
                T *q = pIndices0 + num_indices;
                for (; p != q; p++)
                {
                    const uint32_t key = RG_ETC1_GET_KEY(p);

                    hist[key & 0xFF]++;
                    hist[256 + ((key >> 8) & 0xFF)]++;
                    hist[512 + ((key >> 16) & 0xFF)]++;
                }
            }
            else if (key_size == 2)
            {
                T *p = pIndices0;
                T *q = pIndices0 + (num_indices >> 1) * 2;

                for (; p != q; p += 2)
                {
                    const uint32_t key0 = RG_ETC1_GET_KEY(p);
                    const uint32_t key1 = RG_ETC1_GET_KEY(p + 1);

                    hist[key0 & 0xFF]++;
                    hist[256 + ((key0 >> 8) & 0xFF)]++;

                    hist[key1 & 0xFF]++;
                    hist[256 + ((key1 >> 8) & 0xFF)]++;
                }

                if (num_indices & 1)
                {
                    const uint32_t key = RG_ETC1_GET_KEY(p);

                    hist[key & 0xFF]++;
                    hist[256 + ((key >> 8) & 0xFF)]++;
                }
            }
            else
            {
                RG_ETC1_ASSERT(key_size == 1);
                if (key_size != 1)
                    return NULL;

                T *p = pIndices0;
                T *q = pIndices0 + (num_indices >> 1) * 2;

                for (; p != q; p += 2)
                {
                    const uint32_t key0 = RG_ETC1_GET_KEY(p);
                    const uint32_t key1 = RG_ETC1_GET_KEY(p + 1);

                    hist[key0 & 0xFF]++;
                    hist[key1 & 0xFF]++;
                }

                if (num_indices & 1)
                {
                    const uint32_t key = RG_ETC1_GET_KEY(p);

                    hist[key & 0xFF]++;
                }
            }

            T *pCur = pIndices0;
            T *pNew = pIndices1;

            for (uint32_t pass = 0; pass < key_size; pass++)
            {
                const uint32_t *pHist = &hist[pass << 8];

                uint32_t offsets[256];

                uint32_t cur_ofs = 0;
                for (uint32_t i = 0; i < 256; i += 2)
                {
                    offsets[i] = cur_ofs;
                    cur_ofs += pHist[i];

                    offsets[i + 1] = cur_ofs;
                    cur_ofs += pHist[i + 1];
                }

                const uint32_t pass_shift = pass << 3;

                T *p = pCur;
                T *q = pCur + (num_indices >> 1) * 2;

                for (; p != q; p += 2)
                {
                    uint32_t index0 = p[0];
                    uint32_t index1 = p[1];

                    uint32_t c0 = (RG_ETC1_GET_KEY_FROM_INDEX(index0) >> pass_shift) & 0xFF;
                    uint32_t c1 = (RG_ETC1_GET_KEY_FROM_INDEX(index1) >> pass_shift) & 0xFF;

                    if (c0 == c1)
                    {
                        uint32_t dst_offset0 = offsets[c0];

                        offsets[c0] = dst_offset0 + 2;

                        pNew[dst_offset0] = static_cast<T>(index0);
                        pNew[dst_offset0 + 1] = static_cast<T>(index1);
                    }
                    else
                    {
                        uint32_t dst_offset0 = offsets[c0]++;
                        uint32_t dst_offset1 = offsets[c1]++;

                        pNew[dst_offset0] = static_cast<T>(index0);
                        pNew[dst_offset1] = static_cast<T>(index1);
                    }
                }

                if (num_indices & 1)
                {
                    uint32_t index = *p;
                    uint32_t c = (RG_ETC1_GET_KEY_FROM_INDEX(index) >> pass_shift) & 0xFF;

                    uint32_t dst_offset = offsets[c];
                    offsets[c] = dst_offset + 1;

                    pNew[dst_offset] = static_cast<T>(index);
                }

                T *t = pCur;
                pCur = pNew;
                pNew = t;
            }

            return pCur;
        }

#undef RG_ETC1_GET_KEY
#undef RG_ETC1_GET_KEY_FROM_INDEX

        uint16_t etc1_block::pack_color5(const color_quad_u8 &color, bool scaled, uint32_t bias)
        {
            return pack_color5(color.r, color.g, color.b, scaled, bias);
        }

        uint16_t etc1_block::pack_color5(uint32_t r, uint32_t g, uint32_t b, bool scaled, uint32_t bias)
        {
            if (scaled)
            {
                r = (r * 31U + bias) / 255U;
                g = (g * 31U + bias) / 255U;
                b = (b * 31U + bias) / 255U;
            }

            r = rg_etc1::minimum(r, 31U);
            g = rg_etc1::minimum(g, 31U);
            b = rg_etc1::minimum(b, 31U);

            return static_cast<uint16_t>(b | (g << 5U) | (r << 10U));
        }

        color_quad_u8 etc1_block::unpack_color5(uint16_t packed_color5, bool scaled, uint32_t alpha)
        {
            uint32_t b = packed_color5 & 31U;
            uint32_t g = (packed_color5 >> 5U) & 31U;
            uint32_t r = (packed_color5 >> 10U) & 31U;

            if (scaled)
            {
                b = (b << 3U) | (b >> 2U);
                g = (g << 3U) | (g >> 2U);
                r = (r << 3U) | (r >> 2U);
            }

            return color_quad_u8(cNoClamp, r, g, b, rg_etc1::minimum(alpha, 255U));
        }

        void etc1_block::unpack_color5(uint32_t &r, uint32_t &g, uint32_t &b, uint16_t packed_color5, bool scaled)
        {
            color_quad_u8 c(unpack_color5(packed_color5, scaled, 0));
            r = c.r;
            g = c.g;
            b = c.b;
        }

        bool etc1_block::unpack_color5(color_quad_u8 &result, uint16_t packed_color5, uint16_t packed_delta3, bool scaled, uint32_t alpha)
        {
            int dc_r, dc_g, dc_b;
            unpack_delta3(dc_r, dc_g, dc_b, packed_delta3);

            int b = (packed_color5 & 31U) + dc_b;
            int g = ((packed_color5 >> 5U) & 31U) + dc_g;
            int r = ((packed_color5 >> 10U) & 31U) + dc_r;

            bool success = true;
            if (static_cast<uint32_t>(r | g | b) > 31U)
            {
                success = false;
                r = rg_etc1::clamp<int>(r, 0, 31);
                g = rg_etc1::clamp<int>(g, 0, 31);
                b = rg_etc1::clamp<int>(b, 0, 31);
            }

            if (scaled)
            {
                b = (b << 3U) | (b >> 2U);
                g = (g << 3U) | (g >> 2U);
                r = (r << 3U) | (r >> 2U);
            }

            result.set_noclamp_rgba(r, g, b, rg_etc1::minimum(alpha, 255U));
            return success;
        }

        bool etc1_block::unpack_color5(uint32_t &r, uint32_t &g, uint32_t &b, uint16_t packed_color5, uint16_t packed_delta3, bool scaled, uint32_t alpha)
        {
            color_quad_u8 result;
            const bool success = unpack_color5(result, packed_color5, packed_delta3, scaled, alpha);
            r = result.r;
            g = result.g;
            b = result.b;
            return success;
        }

        uint16_t etc1_block::pack_delta3(int r, int g, int b)
        {
            RG_ETC1_ASSERT((r >= cETC1ColorDeltaMin) && (r <= cETC1ColorDeltaMax));
            RG_ETC1_ASSERT((g >= cETC1ColorDeltaMin) && (g <= cETC1ColorDeltaMax));
            RG_ETC1_ASSERT((b >= cETC1ColorDeltaMin) && (b <= cETC1ColorDeltaMax));
            if (r < 0)
                r += 8;
            if (g < 0)
                g += 8;
            if (b < 0)
                b += 8;
            return static_cast<uint16_t>(b | (g << 3) | (r << 6));
        }

        void etc1_block::unpack_delta3(int &r, int &g, int &b, uint16_t packed_delta3)
        {
            r = (packed_delta3 >> 6) & 7;
            g = (packed_delta3 >> 3) & 7;
            b = packed_delta3 & 7;
            if (r >= 4)
                r -= 8;
            if (g >= 4)
                g -= 8;
            if (b >= 4)
                b -= 8;
        }

        uint16_t etc1_block::pack_color4(const color_quad_u8 &color, bool scaled, uint32_t bias)
        {
            return pack_color4(color.r, color.g, color.b, scaled, bias);
        }

        uint16_t etc1_block::pack_color4(uint32_t r, uint32_t g, uint32_t b, bool scaled, uint32_t bias)
        {
            if (scaled)
            {
                r = (r * 15U + bias) / 255U;
                g = (g * 15U + bias) / 255U;
                b = (b * 15U + bias) / 255U;
            }

            r = rg_etc1::minimum(r, 15U);
            g = rg_etc1::minimum(g, 15U);
            b = rg_etc1::minimum(b, 15U);

            return static_cast<uint16_t>(b | (g << 4U) | (r << 8U));
        }

        color_quad_u8 etc1_block::unpack_color4(uint16_t packed_color4, bool scaled, uint32_t alpha)
        {
            uint32_t b = packed_color4 & 15U;
            uint32_t g = (packed_color4 >> 4U) & 15U;
            uint32_t r = (packed_color4 >> 8U) & 15U;

            if (scaled)
            {
                b = (b << 4U) | b;
                g = (g << 4U) | g;
                r = (r << 4U) | r;
            }

            return color_quad_u8(cNoClamp, r, g, b, rg_etc1::minimum(alpha, 255U));
        }

        void etc1_block::unpack_color4(uint32_t &r, uint32_t &g, uint32_t &b, uint16_t packed_color4, bool scaled)
        {
            color_quad_u8 c(unpack_color4(packed_color4, scaled, 0));
            r = c.r;
            g = c.g;
            b = c.b;
        }

        void etc1_block::get_diff_subblock_colors(color_quad_u8 *pDst, uint16_t packed_color5, uint32_t table_idx)
        {
            RG_ETC1_ASSERT(table_idx < cETC1IntenModifierValues);
            const int *pInten_modifer_table = &g_etc1_inten_tables[table_idx][0];

            uint32_t r, g, b;
            unpack_color5(r, g, b, packed_color5, true);

            const int ir = static_cast<int>(r), ig = static_cast<int>(g), ib = static_cast<int>(b);

            const int y0 = pInten_modifer_table[0];
            pDst[0].set(ir + y0, ig + y0, ib + y0);

            const int y1 = pInten_modifer_table[1];
            pDst[1].set(ir + y1, ig + y1, ib + y1);

            const int y2 = pInten_modifer_table[2];
            pDst[2].set(ir + y2, ig + y2, ib + y2);

            const int y3 = pInten_modifer_table[3];
            pDst[3].set(ir + y3, ig + y3, ib + y3);
        }

        bool etc1_block::get_diff_subblock_colors(color_quad_u8 *pDst, uint16_t packed_color5, uint16_t packed_delta3, uint32_t table_idx)
        {
            RG_ETC1_ASSERT(table_idx < cETC1IntenModifierValues);
            const int *pInten_modifer_table = &g_etc1_inten_tables[table_idx][0];

            uint32_t r, g, b;
            bool success = unpack_color5(r, g, b, packed_color5, packed_delta3, true);

            const int ir = static_cast<int>(r), ig = static_cast<int>(g), ib = static_cast<int>(b);

            const int y0 = pInten_modifer_table[0];
            pDst[0].set(ir + y0, ig + y0, ib + y0);

            const int y1 = pInten_modifer_table[1];
            pDst[1].set(ir + y1, ig + y1, ib + y1);

            const int y2 = pInten_modifer_table[2];
            pDst[2].set(ir + y2, ig + y2, ib + y2);

            const int y3 = pInten_modifer_table[3];
            pDst[3].set(ir + y3, ig + y3, ib + y3);

            return success;
        }

        void etc1_block::get_abs_subblock_colors(color_quad_u8 *pDst, uint16_t packed_color4, uint32_t table_idx)
        {
            RG_ETC1_ASSERT(table_idx < cETC1IntenModifierValues);
            const int *pInten_modifer_table = &g_etc1_inten_tables[table_idx][0];

            uint32_t r, g, b;
            unpack_color4(r, g, b, packed_color4, true);

            const int ir = static_cast<int>(r), ig = static_cast<int>(g), ib = static_cast<int>(b);

            const int y0 = pInten_modifer_table[0];
            pDst[0].set(ir + y0, ig + y0, ib + y0);

            const int y1 = pInten_modifer_table[1];
            pDst[1].set(ir + y1, ig + y1, ib + y1);

            const int y2 = pInten_modifer_table[2];
            pDst[2].set(ir + y2, ig + y2, ib + y2);

            const int y3 = pInten_modifer_table[3];
            pDst[3].set(ir + y3, ig + y3, ib + y3);
        }

        bool unpack_etc1_block(const void *pETC1_block, unsigned int *pDst_pixels_rgba, bool preserve_alpha)
        {
            color_quad_u8 *pDst = reinterpret_cast<color_quad_u8 *>(pDst_pixels_rgba);
            const etc1_block &block = *static_cast<const etc1_block *>(pETC1_block);

            const bool diff_flag = block.get_diff_bit();
            const bool flip_flag = block.get_flip_bit();
            const uint32_t table_index0 = block.get_inten_table(0);
            const uint32_t table_index1 = block.get_inten_table(1);

            color_quad_u8 subblock_colors0[4];
            color_quad_u8 subblock_colors1[4];
            bool success = true;

            if (diff_flag)
            {
                const uint16_t base_color5 = block.get_base5_color();
                const uint16_t delta_color3 = block.get_delta3_color();
                etc1_block::get_diff_subblock_colors(subblock_colors0, base_color5, table_index0);

                if (!etc1_block::get_diff_subblock_colors(subblock_colors1, base_color5, delta_color3, table_index1))
                    success = false;
            }
            else
            {
                const uint16_t base_color4_0 = block.get_base4_color(0);
                etc1_block::get_abs_subblock_colors(subblock_colors0, base_color4_0, table_index0);

                const uint16_t base_color4_1 = block.get_base4_color(1);
                etc1_block::get_abs_subblock_colors(subblock_colors1, base_color4_1, table_index1);
            }

            if (preserve_alpha)
            {
                if (flip_flag)
                {
                    for (uint32_t y = 0; y < 2; y++)
                    {
                        pDst[0].set_rgb(subblock_colors0[block.get_selector(0, y)]);
                        pDst[1].set_rgb(subblock_colors0[block.get_selector(1, y)]);
                        pDst[2].set_rgb(subblock_colors0[block.get_selector(2, y)]);
                        pDst[3].set_rgb(subblock_colors0[block.get_selector(3, y)]);
                        pDst += 4;
                    }

                    for (uint32_t y = 2; y < 4; y++)
                    {
                        pDst[0].set_rgb(subblock_colors1[block.get_selector(0, y)]);
                        pDst[1].set_rgb(subblock_colors1[block.get_selector(1, y)]);
                        pDst[2].set_rgb(subblock_colors1[block.get_selector(2, y)]);
                        pDst[3].set_rgb(subblock_colors1[block.get_selector(3, y)]);
                        pDst += 4;
                    }
                }
                else
                {
                    for (uint32_t y = 0; y < 4; y++)
                    {
                        pDst[0].set_rgb(subblock_colors0[block.get_selector(0, y)]);
                        pDst[1].set_rgb(subblock_colors0[block.get_selector(1, y)]);
                        pDst[2].set_rgb(subblock_colors1[block.get_selector(2, y)]);
                        pDst[3].set_rgb(subblock_colors1[block.get_selector(3, y)]);
                        pDst += 4;
                    }
                }
            }
            else
            {
                if (flip_flag)
                {
                    // 0000
                    // 0000
                    // 1111
                    // 1111
                    for (uint32_t y = 0; y < 2; y++)
                    {
                        pDst[0] = subblock_colors0[block.get_selector(0, y)];
                        pDst[1] = subblock_colors0[block.get_selector(1, y)];
                        pDst[2] = subblock_colors0[block.get_selector(2, y)];
                        pDst[3] = subblock_colors0[block.get_selector(3, y)];
                        pDst += 4;
                    }

                    for (uint32_t y = 2; y < 4; y++)
                    {
                        pDst[0] = subblock_colors1[block.get_selector(0, y)];
                        pDst[1] = subblock_colors1[block.get_selector(1, y)];
                        pDst[2] = subblock_colors1[block.get_selector(2, y)];
                        pDst[3] = subblock_colors1[block.get_selector(3, y)];
                        pDst += 4;
                    }
                }
                else
                {
                    // 0011
                    // 0011
                    // 0011
                    // 0011
                    for (uint32_t y = 0; y < 4; y++)
                    {
                        pDst[0] = subblock_colors0[block.get_selector(0, y)];
                        pDst[1] = subblock_colors0[block.get_selector(1, y)];
                        pDst[2] = subblock_colors1[block.get_selector(2, y)];
                        pDst[3] = subblock_colors1[block.get_selector(3, y)];
                        pDst += 4;
                    }
                }
            }

            return success;
        }

        struct etc1_solution_coordinates
        {
            inline etc1_solution_coordinates()
                : m_unscaled_color(0, 0, 0, 0),
                  m_inten_table(0),
                  m_color4(false)
            {
            }

            inline etc1_solution_coordinates(uint32_t r, uint32_t g, uint32_t b, uint32_t inten_table, bool color4)
                : m_unscaled_color(r, g, b, 255),
                  m_inten_table(inten_table),
                  m_color4(color4)
            {
            }

            inline etc1_solution_coordinates(const color_quad_u8 &c, uint32_t inten_table, bool color4)
                : m_unscaled_color(c),
                  m_inten_table(inten_table),
                  m_color4(color4)
            {
            }

            inline etc1_solution_coordinates(const etc1_solution_coordinates &other)
            {
                *this = other;
            }

            inline etc1_solution_coordinates &operator=(const etc1_solution_coordinates &rhs)
            {
                m_unscaled_color = rhs.m_unscaled_color;
                m_inten_table = rhs.m_inten_table;
                m_color4 = rhs.m_color4;
                return *this;
            }

            inline void clear()
            {
                m_unscaled_color.clear();
                m_inten_table = 0;
                m_color4 = false;
            }

            inline color_quad_u8 get_scaled_color() const
            {
                int br, bg, bb;
                if (m_color4)
                {
                    br = m_unscaled_color.r | (m_unscaled_color.r << 4);
                    bg = m_unscaled_color.g | (m_unscaled_color.g << 4);
                    bb = m_unscaled_color.b | (m_unscaled_color.b << 4);
                }
                else
                {
                    br = (m_unscaled_color.r >> 2) | (m_unscaled_color.r << 3);
                    bg = (m_unscaled_color.g >> 2) | (m_unscaled_color.g << 3);
                    bb = (m_unscaled_color.b >> 2) | (m_unscaled_color.b << 3);
                }
                return color_quad_u8(br, bg, bb);
            }

            inline void get_block_colors(color_quad_u8 *pBlock_colors)
            {
                int br, bg, bb;
                if (m_color4)
                {
                    br = m_unscaled_color.r | (m_unscaled_color.r << 4);
                    bg = m_unscaled_color.g | (m_unscaled_color.g << 4);
                    bb = m_unscaled_color.b | (m_unscaled_color.b << 4);
                }
                else
                {
                    br = (m_unscaled_color.r >> 2) | (m_unscaled_color.r << 3);
                    bg = (m_unscaled_color.g >> 2) | (m_unscaled_color.g << 3);
                    bb = (m_unscaled_color.b >> 2) | (m_unscaled_color.b << 3);
                }
                const int *pInten_table = g_etc1_inten_tables[m_inten_table];
                pBlock_colors[0].set(br + pInten_table[0], bg + pInten_table[0], bb + pInten_table[0]);
                pBlock_colors[1].set(br + pInten_table[1], bg + pInten_table[1], bb + pInten_table[1]);
                pBlock_colors[2].set(br + pInten_table[2], bg + pInten_table[2], bb + pInten_table[2]);
                pBlock_colors[3].set(br + pInten_table[3], bg + pInten_table[3], bb + pInten_table[3]);
            }

            color_quad_u8 m_unscaled_color;
            uint32_t m_inten_table;
            bool m_color4;
        };

        class etc1_optimizer
        {
            etc1_optimizer(const etc1_optimizer &);
            etc1_optimizer &operator=(const etc1_optimizer &);

        public:
            etc1_optimizer()
            {
                clear();
            }

            void clear()
            {
                m_pParams = NULL;
                m_pResult = NULL;
                m_pSorted_luma = NULL;
                m_pSorted_luma_indices = NULL;
            }

            struct params : etc1_pack_params
            {
                params()
                {
                    clear();
                }

                params(const etc1_pack_params &base_params)
                    : etc1_pack_params(base_params)
                {
                    clear_optimizer_params();
                }

                void clear()
                {
                    etc1_pack_params::clear();
                    clear_optimizer_params();
                }

                void clear_optimizer_params()
                {
                    m_num_src_pixels = 0;
                    m_pSrc_pixels = 0;

                    m_use_color4 = false;
                    static const int s_default_scan_delta[] = { 0 };
                    m_pScan_deltas = s_default_scan_delta;
                    m_scan_delta_size = 1;

                    m_base_color5.clear();
                    m_constrain_against_base_color5 = false;
                }

                uint32_t m_num_src_pixels;
                const color_quad_u8 *m_pSrc_pixels;

                bool m_use_color4;
                const int *m_pScan_deltas;
                uint32_t m_scan_delta_size;

                color_quad_u8 m_base_color5;
                bool m_constrain_against_base_color5;
            };

            struct results
            {
                uint64_t m_error;
                color_quad_u8 m_block_color_unscaled;
                uint32_t m_block_inten_table;
                uint32_t m_n;
                uint8_t *m_pSelectors;
                bool m_block_color4;

                inline results &operator=(const results &rhs)
                {
                    m_block_color_unscaled = rhs.m_block_color_unscaled;
                    m_block_color4 = rhs.m_block_color4;
                    m_block_inten_table = rhs.m_block_inten_table;
                    m_error = rhs.m_error;
                    RG_ETC1_ASSERT(m_n == rhs.m_n);
                    memcpy(m_pSelectors, rhs.m_pSelectors, rhs.m_n);
                    return *this;
                }
            };

            void init(const params &params, results &result);
            bool compute();

        private:
            struct potential_solution
            {
                potential_solution()
                    : m_coords(), m_error(cUINT64_MAX), m_valid(false)
                {
                }

                etc1_solution_coordinates m_coords;
                uint8_t m_selectors[8];
                uint64_t m_error;
                bool m_valid;

                void clear()
                {
                    m_coords.clear();
                    m_error = cUINT64_MAX;
                    m_valid = false;
                }
            };

            const params *m_pParams;
            results *m_pResult;

            int m_limit;

            vec3F m_avg_color;
            int m_br, m_bg, m_bb;
            uint16_t m_luma[8];
            uint32_t m_sorted_luma[2][8];
            const uint32_t *m_pSorted_luma_indices;
            uint32_t *m_pSorted_luma;

            uint8_t m_selectors[8];
            uint8_t m_best_selectors[8];

            potential_solution m_best_solution;
            potential_solution m_trial_solution;
            uint8_t m_temp_selectors[8];

            bool evaluate_solution(const etc1_solution_coordinates &coords, potential_solution &trial_solution, potential_solution *pBest_solution);
            bool evaluate_solution_fast(const etc1_solution_coordinates &coords, potential_solution &trial_solution, potential_solution *pBest_solution);
        };

        bool etc1_optimizer::compute()
        {
            const uint32_t n = m_pParams->m_num_src_pixels;
            const int scan_delta_size = m_pParams->m_scan_delta_size;

            // Scan through a subset of the 3D lattice centered around the avg block color trying each 3D (555 or 444) lattice point as a potential block color.
            // Each time a better solution is found try to refine the current solution's block color based of the current selectors and intensity table index.
            for (int zdi = 0; zdi < scan_delta_size; zdi++)
            {
                const int zd = m_pParams->m_pScan_deltas[zdi];
                const int mbb = m_bb + zd;
                if (mbb < 0)
                    continue;
                else if (mbb > m_limit)
                    break;

                for (int ydi = 0; ydi < scan_delta_size; ydi++)
                {
                    const int yd = m_pParams->m_pScan_deltas[ydi];
                    const int mbg = m_bg + yd;
                    if (mbg < 0)
                        continue;
                    else if (mbg > m_limit)
                        break;

                    for (int xdi = 0; xdi < scan_delta_size; xdi++)
                    {
                        const int xd = m_pParams->m_pScan_deltas[xdi];
                        const int mbr = m_br + xd;
                        if (mbr < 0)
                            continue;
                        else if (mbr > m_limit)
                            break;

                        etc1_solution_coordinates coords(mbr, mbg, mbb, 0, m_pParams->m_use_color4);
                        if (m_pParams->m_quality == cHighQuality)
                        {
                            if (!evaluate_solution(coords, m_trial_solution, &m_best_solution))
                                continue;
                        }
                        else
                        {
                            if (!evaluate_solution_fast(coords, m_trial_solution, &m_best_solution))
                                continue;
                        }

                        // Now we have the input block, the avg. color of the input pixels, a set of trial selector indices, and the block color+intensity index.
                        // Now, for each component, attempt to refine the current solution by solving a simple linear equation. For example, for 4 colors:
                        // The goal is:
                        // pixel0 - (block_color+inten_table[selector0]) + pixel1 - (block_color+inten_table[selector1]) + pixel2 - (block_color+inten_table[selector2]) + pixel3 - (block_color+inten_table[selector3]) = 0
                        // Rearranging this:
                        // (pixel0 + pixel1 + pixel2 + pixel3) - (block_color+inten_table[selector0]) - (block_color+inten_table[selector1]) - (block_color+inten_table[selector2]) - (block_color+inten_table[selector3]) = 0
                        // (pixel0 + pixel1 + pixel2 + pixel3) - block_color - inten_table[selector0] - block_color-inten_table[selector1] - block_color-inten_table[selector2] - block_color-inten_table[selector3] = 0
                        // (pixel0 + pixel1 + pixel2 + pixel3) - 4*block_color - inten_table[selector0] - inten_table[selector1] - inten_table[selector2] - inten_table[selector3] = 0
                        // (pixel0 + pixel1 + pixel2 + pixel3) - 4*block_color - (inten_table[selector0] + inten_table[selector1] + inten_table[selector2] + inten_table[selector3]) = 0
                        // (pixel0 + pixel1 + pixel2 + pixel3)/4 - block_color - (inten_table[selector0] + inten_table[selector1] + inten_table[selector2] + inten_table[selector3])/4 = 0
                        // block_color = (pixel0 + pixel1 + pixel2 + pixel3)/4 - (inten_table[selector0] + inten_table[selector1] + inten_table[selector2] + inten_table[selector3])/4
                        // So what this means:
                        // optimal_block_color = avg_input - avg_inten_delta
                        // So the optimal block color can be computed by taking the average block color and subtracting the current average of the intensity delta.
                        // Unfortunately, optimal_block_color must then be quantized to 555 or 444 so it's not always possible to improve matters using this formula.
                        // Also, the above formula is for unclamped intensity deltas. The actual implementation takes into account clamping.

                        const uint32_t max_refinement_trials = (m_pParams->m_quality == cLowQuality) ? 2 : (((xd | yd | zd) == 0) ? 4 : 2);
                        for (uint32_t refinement_trial = 0; refinement_trial < max_refinement_trials; refinement_trial++)
                        {
                            const uint8_t *pSelectors = m_best_solution.m_selectors;
                            const int *pInten_table = g_etc1_inten_tables[m_best_solution.m_coords.m_inten_table];

                            int delta_sum_r = 0, delta_sum_g = 0, delta_sum_b = 0;
                            const color_quad_u8 base_color(m_best_solution.m_coords.get_scaled_color());
                            for (uint32_t r = 0; r < n; r++)
                            {
                                const uint32_t s = *pSelectors++;
                                const int yd2 = pInten_table[s];
                                // Compute actual delta being applied to each pixel, taking into account clamping.
                                delta_sum_r += rg_etc1::clamp<int>(base_color.r + yd2, 0, 255) - base_color.r;
                                delta_sum_g += rg_etc1::clamp<int>(base_color.g + yd2, 0, 255) - base_color.g;
                                delta_sum_b += rg_etc1::clamp<int>(base_color.b + yd2, 0, 255) - base_color.b;
                            }
                            if ((!delta_sum_r) && (!delta_sum_g) && (!delta_sum_b))
                                break;
                            const float avg_delta_r_f = static_cast<float>(delta_sum_r) / n;
                            const float avg_delta_g_f = static_cast<float>(delta_sum_g) / n;
                            const float avg_delta_b_f = static_cast<float>(delta_sum_b) / n;
                            const int br1 = rg_etc1::clamp<int>(static_cast<uint32_t>((m_avg_color[0] - avg_delta_r_f) * m_limit / 255.0f + .5f), 0, m_limit);
                            const int bg1 = rg_etc1::clamp<int>(static_cast<uint32_t>((m_avg_color[1] - avg_delta_g_f) * m_limit / 255.0f + .5f), 0, m_limit);
                            const int bb1 = rg_etc1::clamp<int>(static_cast<uint32_t>((m_avg_color[2] - avg_delta_b_f) * m_limit / 255.0f + .5f), 0, m_limit);

                            bool skip = false;

                            if ((mbr == br1) && (mbg == bg1) && (mbb == bb1))
                                skip = true;
                            else if ((br1 == m_best_solution.m_coords.m_unscaled_color.r) && (bg1 == m_best_solution.m_coords.m_unscaled_color.g) && (bb1 == m_best_solution.m_coords.m_unscaled_color.b))
                                skip = true;
                            else if ((m_br == br1) && (m_bg == bg1) && (m_bb == bb1))
                                skip = true;

                            if (skip)
                                break;

                            etc1_solution_coordinates coords1(br1, bg1, bb1, 0, m_pParams->m_use_color4);
                            if (m_pParams->m_quality == cHighQuality)
                            {
                                if (!evaluate_solution(coords1, m_trial_solution, &m_best_solution))
                                    break;
                            }
                            else
                            {
                                if (!evaluate_solution_fast(coords1, m_trial_solution, &m_best_solution))
                                    break;
                            }

                        } // refinement_trial

                    } // xdi
                }     // ydi
            }         // zdi

            if (!m_best_solution.m_valid)
            {
                m_pResult->m_error = cUINT32_MAX;
                return false;
            }

            const uint8_t *pSelectors = m_best_solution.m_selectors;

#ifdef RG_ETC1_BUILD_DEBUG
            {
                color_quad_u8 block_colors[4];
                m_best_solution.m_coords.get_block_colors(block_colors);

                const color_quad_u8 *pSrc_pixels = m_pParams->m_pSrc_pixels;
                uint64_t actual_error = 0;
                for (uint32_t i = 0; i < n; i++)
                    actual_error += pSrc_pixels[i].squared_distance_rgb(block_colors[pSelectors[i]]);

                RG_ETC1_ASSERT(actual_error == m_best_solution.m_error);
            }
#endif

            m_pResult->m_error = m_best_solution.m_error;

            m_pResult->m_block_color_unscaled = m_best_solution.m_coords.m_unscaled_color;
            m_pResult->m_block_color4 = m_best_solution.m_coords.m_color4;

            m_pResult->m_block_inten_table = m_best_solution.m_coords.m_inten_table;
            memcpy(m_pResult->m_pSelectors, pSelectors, n);
            m_pResult->m_n = n;

            return true;
        }

        void etc1_optimizer::init(const params &p, results &r)
        {
            // This version is hardcoded for 8 pixel subblocks.
            RG_ETC1_ASSERT(p.m_num_src_pixels == 8);

            m_pParams = &p;
            m_pResult = &r;

            const uint32_t n = 8;

            m_limit = m_pParams->m_use_color4 ? 15 : 31;

            vec3F avg_color(0.0f);

            for (uint32_t i = 0; i < n; i++)
            {
                const color_quad_u8 &c = m_pParams->m_pSrc_pixels[i];
                const vec3F fc(c.r, c.g, c.b);

                avg_color += fc;

                m_luma[i] = static_cast<uint16_t>(c.r + c.g + c.b);
                m_sorted_luma[0][i] = i;
            }
            avg_color *= (1.0f / static_cast<float>(n));
            m_avg_color = avg_color;

            m_br = rg_etc1::clamp<int>(static_cast<uint32_t>(m_avg_color[0] * m_limit / 255.0f + .5f), 0, m_limit);
            m_bg = rg_etc1::clamp<int>(static_cast<uint32_t>(m_avg_color[1] * m_limit / 255.0f + .5f), 0, m_limit);
            m_bb = rg_etc1::clamp<int>(static_cast<uint32_t>(m_avg_color[2] * m_limit / 255.0f + .5f), 0, m_limit);

            if (m_pParams->m_quality <= cMediumQuality)
            {
                m_pSorted_luma_indices = indirect_radix_sort(n, m_sorted_luma[0], m_sorted_luma[1], m_luma, 0, sizeof(m_luma[0]), false);
                m_pSorted_luma = m_sorted_luma[0];
                if (m_pSorted_luma_indices == m_sorted_luma[0])
                    m_pSorted_luma = m_sorted_luma[1];

                for (uint32_t i = 0; i < n; i++)
                    m_pSorted_luma[i] = m_luma[m_pSorted_luma_indices[i]];
            }

            m_best_solution.m_coords.clear();
            m_best_solution.m_valid = false;
            m_best_solution.m_error = cUINT64_MAX;
        }

        bool etc1_optimizer::evaluate_solution(const etc1_solution_coordinates &coords, potential_solution &trial_solution, potential_solution *pBest_solution)
        {
            trial_solution.m_valid = false;

            if (m_pParams->m_constrain_against_base_color5)
            {
                const int dr = coords.m_unscaled_color.r - m_pParams->m_base_color5.r;
                const int dg = coords.m_unscaled_color.g - m_pParams->m_base_color5.g;
                const int db = coords.m_unscaled_color.b - m_pParams->m_base_color5.b;

                if ((rg_etc1::minimum(dr, dg, db) < cETC1ColorDeltaMin) || (rg_etc1::maximum(dr, dg, db) > cETC1ColorDeltaMax))
                    return false;
            }

            const color_quad_u8 base_color(coords.get_scaled_color());

            const uint32_t n = 8;

            trial_solution.m_error = cUINT64_MAX;

            for (uint32_t inten_table = 0; inten_table < cETC1IntenModifierValues; inten_table++)
            {
                const int *pInten_table = g_etc1_inten_tables[inten_table];

                color_quad_u8 block_colors[4];
                for (uint32_t s = 0; s < 4; s++)
                {
                    const int yd = pInten_table[s];
                    block_colors[s].set(base_color.r + yd, base_color.g + yd, base_color.b + yd, 0);
                }

                uint64_t total_error = 0;

                const color_quad_u8 *pSrc_pixels = m_pParams->m_pSrc_pixels;
                for (uint32_t c = 0; c < n; c++)
                {
                    const color_quad_u8 &src_pixel = *pSrc_pixels++;

                    uint32_t best_selector_index = 0;
                    uint32_t best_error = rg_etc1::square(src_pixel.r - block_colors[0].r) + rg_etc1::square(src_pixel.g - block_colors[0].g) + rg_etc1::square(src_pixel.b - block_colors[0].b);

                    uint32_t trial_error = rg_etc1::square(src_pixel.r - block_colors[1].r) + rg_etc1::square(src_pixel.g - block_colors[1].g) + rg_etc1::square(src_pixel.b - block_colors[1].b);
                    if (trial_error < best_error)
                    {
                        best_error = trial_error;
                        best_selector_index = 1;
                    }

                    trial_error = rg_etc1::square(src_pixel.r - block_colors[2].r) + rg_etc1::square(src_pixel.g - block_colors[2].g) + rg_etc1::square(src_pixel.b - block_colors[2].b);
                    if (trial_error < best_error)
                    {
                        best_error = trial_error;
                        best_selector_index = 2;
                    }

                    trial_error = rg_etc1::square(src_pixel.r - block_colors[3].r) + rg_etc1::square(src_pixel.g - block_colors[3].g) + rg_etc1::square(src_pixel.b - block_colors[3].b);
                    if (trial_error < best_error)
                    {
                        best_error = trial_error;
                        best_selector_index = 3;
                    }

                    m_temp_selectors[c] = static_cast<uint8_t>(best_selector_index);

                    total_error += best_error;
                    if (total_error >= trial_solution.m_error)
                        break;
                }

                if (total_error < trial_solution.m_error)
                {
                    trial_solution.m_error = total_error;
                    trial_solution.m_coords.m_inten_table = inten_table;
                    memcpy(trial_solution.m_selectors, m_temp_selectors, 8);
                    trial_solution.m_valid = true;
                }
            }
            trial_solution.m_coords.m_unscaled_color = coords.m_unscaled_color;
            trial_solution.m_coords.m_color4 = m_pParams->m_use_color4;

            bool success = false;
            if (pBest_solution)
            {
                if (trial_solution.m_error < pBest_solution->m_error)
                {
                    *pBest_solution = trial_solution;
                    success = true;
                }
            }

            return success;
        }

        bool etc1_optimizer::evaluate_solution_fast(const etc1_solution_coordinates &coords, potential_solution &trial_solution, potential_solution *pBest_solution)
        {
            if (m_pParams->m_constrain_against_base_color5)
            {
                const int dr = coords.m_unscaled_color.r - m_pParams->m_base_color5.r;
                const int dg = coords.m_unscaled_color.g - m_pParams->m_base_color5.g;
                const int db = coords.m_unscaled_color.b - m_pParams->m_base_color5.b;

                if ((rg_etc1::minimum(dr, dg, db) < cETC1ColorDeltaMin) || (rg_etc1::maximum(dr, dg, db) > cETC1ColorDeltaMax))
                {
                    trial_solution.m_valid = false;
                    return false;
                }
            }

            const color_quad_u8 base_color(coords.get_scaled_color());

            const uint32_t n = 8;

            trial_solution.m_error = cUINT64_MAX;

            for (int inten_table = cETC1IntenModifierValues - 1; inten_table >= 0; --inten_table)
            {
                const int *pInten_table = g_etc1_inten_tables[inten_table];

                uint32_t block_inten[4];
                color_quad_u8 block_colors[4];
                for (uint32_t s = 0; s < 4; s++)
                {
                    const int yd = pInten_table[s];
                    color_quad_u8 block_color(base_color.r + yd, base_color.g + yd, base_color.b + yd, 0);
                    block_colors[s] = block_color;
                    block_inten[s] = block_color.r + block_color.g + block_color.b;
                }

                // evaluate_solution_fast() enforces/assumesd a total ordering of the input colors along the intensity (1,1,1) axis to more quickly classify the inputs to selectors.
                // The inputs colors have been presorted along the projection onto this axis, and ETC1 block colors are always ordered along the intensity axis, so this classification is fast.
                // 0   1   2   3
                //   01  12  23
                const uint32_t block_inten_midpoints[3] = { block_inten[0] + block_inten[1], block_inten[1] + block_inten[2], block_inten[2] + block_inten[3] };

                uint64_t total_error = 0;
                const color_quad_u8 *pSrc_pixels = m_pParams->m_pSrc_pixels;
                if ((m_pSorted_luma[n - 1] * 2) < block_inten_midpoints[0])
                {
                    if (block_inten[0] > m_pSorted_luma[n - 1])
                    {
                        const uint32_t min_error = static_cast<uint32_t>(labs(block_inten[0] - m_pSorted_luma[n - 1]));
                        if (min_error >= trial_solution.m_error)
                            continue;
                    }

                    memset(&m_temp_selectors[0], 0, n);

                    for (uint32_t c = 0; c < n; c++)
                        total_error += block_colors[0].squared_distance_rgb(pSrc_pixels[c]);
                }
                else if ((m_pSorted_luma[0] * 2) >= block_inten_midpoints[2])
                {
                    if (m_pSorted_luma[0] > block_inten[3])
                    {
                        const uint32_t min_error = static_cast<uint32_t>(labs(m_pSorted_luma[0] - block_inten[3]));
                        if (min_error >= trial_solution.m_error)
                            continue;
                    }

                    memset(&m_temp_selectors[0], 3, n);

                    for (uint32_t c = 0; c < n; c++)
                        total_error += block_colors[3].squared_distance_rgb(pSrc_pixels[c]);
                }
                else
                {
                    uint32_t cur_selector = 0, c;
                    for (c = 0; c < n; c++)
                    {
                        const uint32_t y = m_pSorted_luma[c];
                        while ((y * 2) >= block_inten_midpoints[cur_selector])
                            if (++cur_selector > 2)
                                goto done;
                        const uint32_t sorted_pixel_index = m_pSorted_luma_indices[c];
                        m_temp_selectors[sorted_pixel_index] = static_cast<uint8_t>(cur_selector);
                        total_error += block_colors[cur_selector].squared_distance_rgb(pSrc_pixels[sorted_pixel_index]);
                    }
                done:
                    while (c < n)
                    {
                        const uint32_t sorted_pixel_index = m_pSorted_luma_indices[c];
                        m_temp_selectors[sorted_pixel_index] = 3;
                        total_error += block_colors[3].squared_distance_rgb(pSrc_pixels[sorted_pixel_index]);
                        ++c;
                    }
                }

                if (total_error < trial_solution.m_error)
                {
                    trial_solution.m_error = total_error;
                    trial_solution.m_coords.m_inten_table = inten_table;
                    memcpy(trial_solution.m_selectors, m_temp_selectors, n);
                    trial_solution.m_valid = true;
                    if (!total_error)
                        break;
                }
            }
            trial_solution.m_coords.m_unscaled_color = coords.m_unscaled_color;
            trial_solution.m_coords.m_color4 = m_pParams->m_use_color4;

            bool success = false;
            if (pBest_solution)
            {
                if (trial_solution.m_error < pBest_solution->m_error)
                {
                    *pBest_solution = trial_solution;
                    success = true;
                }
            }

            return success;
        }

        static uint32_t etc1_decode_value(uint32_t diff, uint32_t inten, uint32_t selector, uint32_t packed_c)
        {
            const uint32_t limit = diff ? 32 : 16;
            VOGL_NOTE_UNUSED(limit);
            RG_ETC1_ASSERT((diff < 2) && (inten < 8) && (selector < 4) && (packed_c < limit));
            int c;
            if (diff)
                c = (packed_c >> 2) | (packed_c << 3);
            else
                c = packed_c | (packed_c << 4);
            c += g_etc1_inten_tables[inten][selector];
            c = rg_etc1::clamp<int>(c, 0, 255);
            return c;
        }

        static inline int mul_8bit(int a, int b)
        {
            int t = a * b + 128;
            return (t + (t >> 8)) >> 8;
        }

        void pack_etc1_block_init()
        {
            for (uint32_t diff = 0; diff < 2; diff++)
            {
                const uint32_t limit = diff ? 32 : 16;

                for (uint32_t inten = 0; inten < 8; inten++)
                {
                    for (uint32_t selector = 0; selector < 4; selector++)
                    {
                        const uint32_t inverse_table_index = diff + (inten << 1) + (selector << 4);
                        for (uint32_t color = 0; color < 256; color++)
                        {
                            uint32_t best_error = cUINT32_MAX, best_packed_c = 0;
                            for (uint32_t packed_c = 0; packed_c < limit; packed_c++)
                            {
                                int v = etc1_decode_value(diff, inten, selector, packed_c);
                                uint32_t err = static_cast<uint32_t>(labs(v - static_cast<int>(color)));
                                if (err < best_error)
                                {
                                    best_error = err;
                                    best_packed_c = packed_c;
                                    if (!best_error)
                                        break;
                                }
                            }
                            RG_ETC1_ASSERT(best_error <= 255);
                            g_etc1_inverse_lookup[inverse_table_index][color] = static_cast<uint16_t>(best_packed_c | (best_error << 8));
                        }
                    }
                }
            }

            uint32_t expand5[32];
            for (int i = 0; i < 32; i++)
                expand5[i] = (i << 3) | (i >> 2);

            for (int i = 0; i < 256 + 16; i++)
            {
                int v = clamp<int>(i - 8, 0, 255);
                g_quant5_tab[i] = static_cast<uint8_t>(expand5[mul_8bit(v, 31)]);
            }
        }

        // Packs solid color blocks efficiently using a set of small precomputed tables.
        // For random 888 inputs, MSE results are better than Erricson's ETC1 packer in "slow" mode ~9.5% of the time, is slightly worse only ~.01% of the time, and is equal the rest of the time.
        static uint64_t pack_etc1_block_solid_color(etc1_block &block, const uint8_t *pColor, etc1_pack_params &pack_params)
        {
            VOGL_NOTE_UNUSED(pack_params);
            RG_ETC1_ASSERT(g_etc1_inverse_lookup[0][255]);

            static uint32_t s_next_comp[4] = { 1, 2, 0, 1 };

            uint32_t best_error = cUINT32_MAX, best_i = 0;
            int best_x = 0, best_packed_c1 = 0, best_packed_c2 = 0;

            // For each possible 8-bit value, there is a precomputed list of diff/inten/selector configurations that allow that 8-bit value to be encoded with no error.
            for (uint32_t i = 0; i < 3; i++)
            {
                const uint32_t c1 = pColor[s_next_comp[i]], c2 = pColor[s_next_comp[i + 1]];

                const int delta_range = 1;
                for (int delta = -delta_range; delta <= delta_range; delta++)
                {
                    const int c_plus_delta = rg_etc1::clamp<int>(pColor[i] + delta, 0, 255);

                    const uint16_t *pTable;
                    if (!c_plus_delta)
                        pTable = g_color8_to_etc_block_config_0_255[0];
                    else if (c_plus_delta == 255)
                        pTable = g_color8_to_etc_block_config_0_255[1];
                    else
                        pTable = g_color8_to_etc_block_config_1_to_254[c_plus_delta - 1];

                    do
                    {
                        const uint32_t x = *pTable++;

#ifdef RG_ETC1_BUILD_DEBUG
                        const uint32_t diff = x & 1;
                        const uint32_t inten = (x >> 1) & 7;
                        const uint32_t selector = (x >> 4) & 3;
                        const uint32_t p0 = (x >> 8) & 255;
                        RG_ETC1_ASSERT(etc1_decode_value(diff, inten, selector, p0) == (uint32_t)c_plus_delta);
#endif

                        const uint16_t *pInverse_table = g_etc1_inverse_lookup[x & 0xFF];
                        uint16_t p1 = pInverse_table[c1];
                        uint16_t p2 = pInverse_table[c2];
                        const uint32_t trial_error = rg_etc1::square(c_plus_delta - pColor[i]) + rg_etc1::square(p1 >> 8) + rg_etc1::square(p2 >> 8);
                        if (trial_error < best_error)
                        {
                            best_error = trial_error;
                            best_x = x;
                            best_packed_c1 = p1 & 0xFF;
                            best_packed_c2 = p2 & 0xFF;
                            best_i = i;
                            if (!best_error)
                                goto found_perfect_match;
                        }
                    } while (*pTable != 0xFFFF);
                }
            }
        found_perfect_match:

            const uint32_t diff = best_x & 1;
            const uint32_t inten = (best_x >> 1) & 7;

            block.m_bytes[3] = static_cast<uint8_t>(((inten | (inten << 3)) << 2) | (diff << 1));

            const uint32_t etc1_selector = g_selector_index_to_etc1[(best_x >> 4) & 3];
            *reinterpret_cast<uint16_t *>(&block.m_bytes[4]) = (etc1_selector & 2) ? 0xFFFF : 0;
            *reinterpret_cast<uint16_t *>(&block.m_bytes[6]) = (etc1_selector & 1) ? 0xFFFF : 0;

            const uint32_t best_packed_c0 = (best_x >> 8) & 255;
            if (diff)
            {
                block.m_bytes[best_i] = static_cast<uint8_t>(best_packed_c0 << 3);
                block.m_bytes[s_next_comp[best_i]] = static_cast<uint8_t>(best_packed_c1 << 3);
                block.m_bytes[s_next_comp[best_i + 1]] = static_cast<uint8_t>(best_packed_c2 << 3);
            }
            else
            {
                block.m_bytes[best_i] = static_cast<uint8_t>(best_packed_c0 | (best_packed_c0 << 4));
                block.m_bytes[s_next_comp[best_i]] = static_cast<uint8_t>(best_packed_c1 | (best_packed_c1 << 4));
                block.m_bytes[s_next_comp[best_i + 1]] = static_cast<uint8_t>(best_packed_c2 | (best_packed_c2 << 4));
            }

            return best_error;
        }

        static uint32_t pack_etc1_block_solid_color_constrained(
            etc1_optimizer::results &results,
            uint32_t num_colors, const uint8_t *pColor,
            etc1_pack_params &pack_params,
            bool use_diff,
            const color_quad_u8 *pBase_color5_unscaled)
        {
            RG_ETC1_ASSERT(g_etc1_inverse_lookup[0][255]);

            VOGL_NOTE_UNUSED(pack_params);
            static uint32_t s_next_comp[4] = { 1, 2, 0, 1 };

            uint32_t best_error = cUINT32_MAX, best_i = 0;
            int best_x = 0, best_packed_c1 = 0, best_packed_c2 = 0;

            // For each possible 8-bit value, there is a precomputed list of diff/inten/selector configurations that allow that 8-bit value to be encoded with no error.
            for (uint32_t i = 0; i < 3; i++)
            {
                const uint32_t c1 = pColor[s_next_comp[i]], c2 = pColor[s_next_comp[i + 1]];

                const int delta_range = 1;
                for (int delta = -delta_range; delta <= delta_range; delta++)
                {
                    const int c_plus_delta = rg_etc1::clamp<int>(pColor[i] + delta, 0, 255);

                    const uint16_t *pTable;
                    if (!c_plus_delta)
                        pTable = g_color8_to_etc_block_config_0_255[0];
                    else if (c_plus_delta == 255)
                        pTable = g_color8_to_etc_block_config_0_255[1];
                    else
                        pTable = g_color8_to_etc_block_config_1_to_254[c_plus_delta - 1];

                    do
                    {
                        const uint32_t x = *pTable++;
                        const uint32_t diff = x & 1;
                        if (static_cast<uint32_t>(use_diff) != diff)
                        {
                            if (*pTable == 0xFFFF)
                                break;
                            continue;
                        }

                        if ((diff) && (pBase_color5_unscaled))
                        {
                            const int p0 = (x >> 8) & 255;
                            int delta2 = p0 - static_cast<int>(pBase_color5_unscaled->c[i]);
                            if ((delta2 < cETC1ColorDeltaMin) || (delta2 > cETC1ColorDeltaMax))
                            {
                                if (*pTable == 0xFFFF)
                                    break;
                                continue;
                            }
                        }

#ifdef RG_ETC1_BUILD_DEBUG
                        {
                            const uint32_t inten = (x >> 1) & 7;
                            const uint32_t selector = (x >> 4) & 3;
                            const uint32_t p0 = (x >> 8) & 255;
                            RG_ETC1_ASSERT(etc1_decode_value(diff, inten, selector, p0) == (uint32_t)c_plus_delta);
                        }
#endif

                        const uint16_t *pInverse_table = g_etc1_inverse_lookup[x & 0xFF];
                        uint16_t p1 = pInverse_table[c1];
                        uint16_t p2 = pInverse_table[c2];

                        if ((diff) && (pBase_color5_unscaled))
                        {
                            int delta1 = (p1 & 0xFF) - static_cast<int>(pBase_color5_unscaled->c[s_next_comp[i]]);
                            int delta2 = (p2 & 0xFF) - static_cast<int>(pBase_color5_unscaled->c[s_next_comp[i + 1]]);
                            if ((delta1 < cETC1ColorDeltaMin) || (delta1 > cETC1ColorDeltaMax) || (delta2 < cETC1ColorDeltaMin) || (delta2 > cETC1ColorDeltaMax))
                            {
                                if (*pTable == 0xFFFF)
                                    break;
                                continue;
                            }
                        }

                        const uint32_t trial_error = rg_etc1::square(c_plus_delta - pColor[i]) + rg_etc1::square(p1 >> 8) + rg_etc1::square(p2 >> 8);
                        if (trial_error < best_error)
                        {
                            best_error = trial_error;
                            best_x = x;
                            best_packed_c1 = p1 & 0xFF;
                            best_packed_c2 = p2 & 0xFF;
                            best_i = i;
                            if (!best_error)
                                goto found_perfect_match;
                        }
                    } while (*pTable != 0xFFFF);
                }
            }
        found_perfect_match:

            if (best_error == cUINT32_MAX)
                return best_error;

            best_error *= num_colors;

            results.m_n = num_colors;
            results.m_block_color4 = !(best_x & 1);
            results.m_block_inten_table = (best_x >> 1) & 7;
            memset(results.m_pSelectors, (best_x >> 4) & 3, num_colors);

            const uint32_t best_packed_c0 = (best_x >> 8) & 255;
            results.m_block_color_unscaled[best_i] = static_cast<uint8_t>(best_packed_c0);
            results.m_block_color_unscaled[s_next_comp[best_i]] = static_cast<uint8_t>(best_packed_c1);
            results.m_block_color_unscaled[s_next_comp[best_i + 1]] = static_cast<uint8_t>(best_packed_c2);
            results.m_error = best_error;

            return best_error;
        }

        // Function originally from RYG's public domain real-time DXT1 compressor, modified for 555.
        static void dither_block_555(color_quad_u8 *dest, const color_quad_u8 *block)
        {
            int err[8], *ep1 = err, *ep2 = err + 4;
            uint8_t *quant = g_quant5_tab + 8;

            memset(dest, 0xFF, sizeof(color_quad_u8) * 16);

            // process channels seperately
            for (int ch = 0; ch < 3; ch++)
            {
                uint8_t *bp = (uint8_t *)block;
                uint8_t *dp = (uint8_t *)dest;

                bp += ch;
                dp += ch;

                memset(err, 0, sizeof(err));
                for (int y = 0; y < 4; y++)
                {
                    // pixel 0
                    dp[0] = quant[bp[0] + ((3 * ep2[1] + 5 * ep2[0]) >> 4)];
                    ep1[0] = bp[0] - dp[0];

                    // pixel 1
                    dp[4] = quant[bp[4] + ((7 * ep1[0] + 3 * ep2[2] + 5 * ep2[1] + ep2[0]) >> 4)];
                    ep1[1] = bp[4] - dp[4];

                    // pixel 2
                    dp[8] = quant[bp[8] + ((7 * ep1[1] + 3 * ep2[3] + 5 * ep2[2] + ep2[1]) >> 4)];
                    ep1[2] = bp[8] - dp[8];

                    // pixel 3
                    dp[12] = quant[bp[12] + ((7 * ep1[2] + 5 * ep2[3] + ep2[2]) >> 4)];
                    ep1[3] = bp[12] - dp[12];

                    // advance to next line
                    int *tmp = ep1;
                    ep1 = ep2;
                    ep2 = tmp;
                    bp += 16;
                    dp += 16;
                }
            }
        }

        unsigned int pack_etc1_block(void *pETC1_block, const unsigned int *pSrc_pixels_rgba, etc1_pack_params &pack_params)
        {
            const color_quad_u8 *pSrc_pixels = reinterpret_cast<const color_quad_u8 *>(pSrc_pixels_rgba);
            etc1_block &dst_block = *static_cast<etc1_block *>(pETC1_block);

#ifdef RG_ETC1_BUILD_DEBUG
            // Ensure all alpha values are 0xFF.
            for (uint32_t i = 0; i < 16; i++)
            {
                RG_ETC1_ASSERT(pSrc_pixels[i].a == 255);
            }
#endif

            color_quad_u8 src_pixel0(pSrc_pixels[0]);

            // Check for solid block.
            const uint32_t first_pixel_u32 = pSrc_pixels->m_u32;
            int r;
            for (r = 15; r >= 1; --r)
                if (pSrc_pixels[r].m_u32 != first_pixel_u32)
                    break;
            if (!r)
                return static_cast<unsigned int>(16 * pack_etc1_block_solid_color(dst_block, &pSrc_pixels[0].r, pack_params));

            color_quad_u8 dithered_pixels[16];
            if (pack_params.m_dithering)
            {
                dither_block_555(dithered_pixels, pSrc_pixels);
                pSrc_pixels = dithered_pixels;
            }

            etc1_optimizer optimizer;

            uint64_t best_error = cUINT64_MAX;
            uint32_t best_flip = false, best_use_color4 = false;

            uint8_t best_selectors[2][8];
            etc1_optimizer::results best_results[2];
            for (uint32_t i = 0; i < 2; i++)
            {
                best_results[i].m_n = 8;
                best_results[i].m_pSelectors = best_selectors[i];
            }

            uint8_t selectors[3][8];
            etc1_optimizer::results results[3];

            for (uint32_t i = 0; i < 3; i++)
            {
                results[i].m_n = 8;
                results[i].m_pSelectors = selectors[i];
            }

            color_quad_u8 subblock_pixels[8];

            etc1_optimizer::params params(pack_params);
            params.m_num_src_pixels = 8;
            params.m_pSrc_pixels = subblock_pixels;

            for (uint32_t flip = 0; flip < 2; flip++)
            {
                for (uint32_t use_color4 = 0; use_color4 < 2; use_color4++)
                {
                    uint64_t trial_error = 0;

                    uint32_t subblock;
                    for (subblock = 0; subblock < 2; subblock++)
                    {
                        if (flip)
                            memcpy(subblock_pixels, pSrc_pixels + subblock * 8, sizeof(color_quad_u8) * 8);
                        else
                        {
                            const color_quad_u8 *pSrc_col = pSrc_pixels + subblock * 2;
                            subblock_pixels[0] = pSrc_col[0];
                            subblock_pixels[1] = pSrc_col[4];
                            subblock_pixels[2] = pSrc_col[8];
                            subblock_pixels[3] = pSrc_col[12];
                            subblock_pixels[4] = pSrc_col[1];
                            subblock_pixels[5] = pSrc_col[5];
                            subblock_pixels[6] = pSrc_col[9];
                            subblock_pixels[7] = pSrc_col[13];
                        }

                        results[2].m_error = cUINT64_MAX;
                        if ((params.m_quality >= cMediumQuality) && ((subblock) || (use_color4)))
                        {
                            const uint32_t subblock_pixel0_u32 = subblock_pixels[0].m_u32;
                            for (r = 7; r >= 1; --r)
                                if (subblock_pixels[r].m_u32 != subblock_pixel0_u32)
                                    break;
                            if (!r)
                            {
                                pack_etc1_block_solid_color_constrained(results[2], 8, &subblock_pixels[0].r, pack_params, !use_color4, (subblock && !use_color4) ? &results[0].m_block_color_unscaled : NULL);
                            }
                        }

                        params.m_use_color4 = (use_color4 != 0);
                        params.m_constrain_against_base_color5 = false;

                        if ((!use_color4) && (subblock))
                        {
                            params.m_constrain_against_base_color5 = true;
                            params.m_base_color5 = results[0].m_block_color_unscaled;
                        }

                        if (params.m_quality == cHighQuality)
                        {
                            static const int s_scan_delta_0_to_4[] = { -4, -3, -2, -1, 0, 1, 2, 3, 4 };
                            params.m_scan_delta_size = RG_ETC1_ARRAY_SIZE(s_scan_delta_0_to_4);
                            params.m_pScan_deltas = s_scan_delta_0_to_4;
                        }
                        else if (params.m_quality == cMediumQuality)
                        {
                            static const int s_scan_delta_0_to_1[] = { -1, 0, 1 };
                            params.m_scan_delta_size = RG_ETC1_ARRAY_SIZE(s_scan_delta_0_to_1);
                            params.m_pScan_deltas = s_scan_delta_0_to_1;
                        }
                        else
                        {
                            static const int s_scan_delta_0[] = { 0 };
                            params.m_scan_delta_size = RG_ETC1_ARRAY_SIZE(s_scan_delta_0);
                            params.m_pScan_deltas = s_scan_delta_0;
                        }

                        optimizer.init(params, results[subblock]);
                        if (!optimizer.compute())
                            break;

                        if (params.m_quality >= cMediumQuality)
                        {
                            // TODO: Fix fairly arbitrary/unrefined thresholds that control how far away to scan for potentially better solutions.
                            const uint32_t refinement_error_thresh0 = 3000;
                            const uint32_t refinement_error_thresh1 = 6000;
                            if (results[subblock].m_error > refinement_error_thresh0)
                            {
                                if (params.m_quality == cMediumQuality)
                                {
                                    static const int s_scan_delta_2_to_3[] = { -3, -2, 2, 3 };
                                    params.m_scan_delta_size = RG_ETC1_ARRAY_SIZE(s_scan_delta_2_to_3);
                                    params.m_pScan_deltas = s_scan_delta_2_to_3;
                                }
                                else
                                {
                                    static const int s_scan_delta_5_to_5[] = { -5, 5 };
                                    static const int s_scan_delta_5_to_8[] = { -8, -7, -6, -5, 5, 6, 7, 8 };
                                    if (results[subblock].m_error > refinement_error_thresh1)
                                    {
                                        params.m_scan_delta_size = RG_ETC1_ARRAY_SIZE(s_scan_delta_5_to_8);
                                        params.m_pScan_deltas = s_scan_delta_5_to_8;
                                    }
                                    else
                                    {
                                        params.m_scan_delta_size = RG_ETC1_ARRAY_SIZE(s_scan_delta_5_to_5);
                                        params.m_pScan_deltas = s_scan_delta_5_to_5;
                                    }
                                }

                                if (!optimizer.compute())
                                    break;
                            }

                            if (results[2].m_error < results[subblock].m_error)
                                results[subblock] = results[2];
                        }

                        trial_error += results[subblock].m_error;
                        if (trial_error >= best_error)
                            break;
                    }

                    if (subblock < 2)
                        continue;

                    best_error = trial_error;
                    best_results[0] = results[0];
                    best_results[1] = results[1];
                    best_flip = flip;
                    best_use_color4 = use_color4;

                } // use_color4

            } // flip

            int dr = best_results[1].m_block_color_unscaled.r - best_results[0].m_block_color_unscaled.r;
            int dg = best_results[1].m_block_color_unscaled.g - best_results[0].m_block_color_unscaled.g;
            int db = best_results[1].m_block_color_unscaled.b - best_results[0].m_block_color_unscaled.b;
            RG_ETC1_ASSERT(best_use_color4 || ((rg_etc1::minimum(dr, dg, db) >= cETC1ColorDeltaMin) && (rg_etc1::maximum(dr, dg, db) <= cETC1ColorDeltaMax)));

            if (best_use_color4)
            {
                dst_block.m_bytes[0] = static_cast<uint8_t>(best_results[1].m_block_color_unscaled.r | (best_results[0].m_block_color_unscaled.r << 4));
                dst_block.m_bytes[1] = static_cast<uint8_t>(best_results[1].m_block_color_unscaled.g | (best_results[0].m_block_color_unscaled.g << 4));
                dst_block.m_bytes[2] = static_cast<uint8_t>(best_results[1].m_block_color_unscaled.b | (best_results[0].m_block_color_unscaled.b << 4));
            }
            else
            {
                if (dr < 0)
                    dr += 8;
                dst_block.m_bytes[0] = static_cast<uint8_t>((best_results[0].m_block_color_unscaled.r << 3) | dr);
                if (dg < 0)
                    dg += 8;
                dst_block.m_bytes[1] = static_cast<uint8_t>((best_results[0].m_block_color_unscaled.g << 3) | dg);
                if (db < 0)
                    db += 8;
                dst_block.m_bytes[2] = static_cast<uint8_t>((best_results[0].m_block_color_unscaled.b << 3) | db);
            }

            dst_block.m_bytes[3] = static_cast<uint8_t>((best_results[1].m_block_inten_table << 2) | (best_results[0].m_block_inten_table << 5) | ((~best_use_color4 & 1) << 1) | best_flip);

            uint32_t selector0 = 0, selector1 = 0;
            if (best_flip)
            {
                // flipped:
                // { 0, 0 }, { 1, 0 }, { 2, 0 }, { 3, 0 },
                // { 0, 1 }, { 1, 1 }, { 2, 1 }, { 3, 1 }
                //
                // { 0, 2 }, { 1, 2 }, { 2, 2 }, { 3, 2 },
                // { 0, 3 }, { 1, 3 }, { 2, 3 }, { 3, 3 }
                const uint8_t *pSelectors0 = best_results[0].m_pSelectors;
                const uint8_t *pSelectors1 = best_results[1].m_pSelectors;
                for (int x = 3; x >= 0; --x)
                {
                    uint32_t b;
                    b = g_selector_index_to_etc1[pSelectors1[4 + x]];
                    selector0 = (selector0 << 1) | (b & 1);
                    selector1 = (selector1 << 1) | (b >> 1);

                    b = g_selector_index_to_etc1[pSelectors1[x]];
                    selector0 = (selector0 << 1) | (b & 1);
                    selector1 = (selector1 << 1) | (b >> 1);

                    b = g_selector_index_to_etc1[pSelectors0[4 + x]];
                    selector0 = (selector0 << 1) | (b & 1);
                    selector1 = (selector1 << 1) | (b >> 1);

                    b = g_selector_index_to_etc1[pSelectors0[x]];
                    selector0 = (selector0 << 1) | (b & 1);
                    selector1 = (selector1 << 1) | (b >> 1);
                }
            }
            else
            {
                // non-flipped:
                // { 0, 0 }, { 0, 1 }, { 0, 2 }, { 0, 3 },
                // { 1, 0 }, { 1, 1 }, { 1, 2 }, { 1, 3 }
                //
                // { 2, 0 }, { 2, 1 }, { 2, 2 }, { 2, 3 },
                // { 3, 0 }, { 3, 1 }, { 3, 2 }, { 3, 3 }
                for (int subblock = 1; subblock >= 0; --subblock)
                {
                    const uint8_t *pSelectors = best_results[subblock].m_pSelectors + 4;
                    for (uint32_t i = 0; i < 2; i++)
                    {
                        uint32_t b;
                        b = g_selector_index_to_etc1[pSelectors[3]];
                        selector0 = (selector0 << 1) | (b & 1);
                        selector1 = (selector1 << 1) | (b >> 1);

                        b = g_selector_index_to_etc1[pSelectors[2]];
                        selector0 = (selector0 << 1) | (b & 1);
                        selector1 = (selector1 << 1) | (b >> 1);

                        b = g_selector_index_to_etc1[pSelectors[1]];
                        selector0 = (selector0 << 1) | (b & 1);
                        selector1 = (selector1 << 1) | (b >> 1);

                        b = g_selector_index_to_etc1[pSelectors[0]];
                        selector0 = (selector0 << 1) | (b & 1);
                        selector1 = (selector1 << 1) | (b >> 1);

                        pSelectors -= 4;
                    }
                }
            }

            dst_block.m_bytes[4] = static_cast<uint8_t>(selector1 >> 8);
            dst_block.m_bytes[5] = static_cast<uint8_t>(selector1 & 0xFF);
            dst_block.m_bytes[6] = static_cast<uint8_t>(selector0 >> 8);
            dst_block.m_bytes[7] = static_cast<uint8_t>(selector0 & 0xFF);

            return static_cast<unsigned int>(best_error);
        }

    } // namespace rg_etc1

} // namespace vogl
